From 178ada23f811354e47683677ab0c787c6170750e Mon Sep 17 00:00:00 2001
From: George <gyuton@yandex-team.ru>
Date: Wed, 10 Feb 2021 15:55:18 +0300
Subject: [PATCH 01/19] early draft

---
 .../functions/tuple-map-functions.md          | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/docs/en/sql-reference/functions/tuple-map-functions.md b/docs/en/sql-reference/functions/tuple-map-functions.md
index a46c36395b8..50015cd996e 100644
--- a/docs/en/sql-reference/functions/tuple-map-functions.md
+++ b/docs/en/sql-reference/functions/tuple-map-functions.md
@@ -112,4 +112,34 @@ Result:
 └──────────────────────────────┴───────────────────────────────────┘
 ```
 
+## mapContains {#mapcontains}
+
+Determines  whether `map.keys` contains the `key` parameter.
+
+**Syntax**
+
+``` sql
+mapContains(map, key)
+```
+
+**Parameters** 
+
+-   `map` — Map. [Type name](relative/path/to/type/dscr.md#type).
+-   `key` — Key. Type matches the type of `map.keys`.
+
+**Returned value**
+
+-   `1` if `map.keys` contains `key`, `0` if not.
+
+Type: [UInt8](../../sql-reference/data-types/int-uint.md).
+
+**Example**
+
+Query:
+
+
+## mapKeys {#mapKeys}
+
+## mapValues {#mapvalues}
+
 [Original article](https://clickhouse.tech/docs/en/query_language/functions/tuple-map-functions/) <!--hide-->

From b574d8331b2cd6c2cd8dfe7d36ad8257b392db83 Mon Sep 17 00:00:00 2001
From: George <gyuton@yandex-team.ru>
Date: Thu, 11 Feb 2021 11:46:31 +0300
Subject: [PATCH 02/19] Updated description

---
 .../functions/tuple-map-functions.md          | 97 ++++++++++++++++++-
 1 file changed, 96 insertions(+), 1 deletion(-)

diff --git a/docs/en/sql-reference/functions/tuple-map-functions.md b/docs/en/sql-reference/functions/tuple-map-functions.md
index 50015cd996e..d3503937af2 100644
--- a/docs/en/sql-reference/functions/tuple-map-functions.md
+++ b/docs/en/sql-reference/functions/tuple-map-functions.md
@@ -137,9 +137,104 @@ Type: [UInt8](../../sql-reference/data-types/int-uint.md).
 
 Query:
 
+```sql
+CREATE TABLE test (a Map(String,String)) ENGINE = Memory;
 
-## mapKeys {#mapKeys}
+INSERT INTO test VALUES ({'name':'eleven','age':'11'}), ({'number':'twelve','position':'6.0'});
+
+SELECT mapContains(a, 'name') FROM test;
+
+```
+
+Result:
+
+```text
+┌─mapContains(a, 'name')─┐
+│                      1 │
+│                      0 │
+└────────────────────────┘
+```
+
+## mapKeys {#mapkeys}
+
+Returns all the keys from `map` parameter.
+
+**Syntax**
+
+```sql
+mapKeys(map)
+```
+
+**Parameters**
+
+-   `map`- Map.
+
+**Returned value**
+
+-   Array containing all the keys from `map`.
+
+Type: [Array](../../sql-reference/data-types/array.md).
+
+**Example**
+
+Query:
+
+```sql
+CREATE TABLE test (a Map(String,String)) ENGINE = Memory;
+
+INSERT INTO test VALUES ({'name':'eleven','age':'11'}), ({'number':'twelve','position':'6.0'});
+
+SELECT mapKeys(a) FROM test;
+```
+
+Result:
+
+```text
+┌─mapKeys(a)────────────┐
+│ ['name','age']        │
+│ ['number','position'] │
+└───────────────────────┘
+```
 
 ## mapValues {#mapvalues}
 
+Returns all the values from `map` parameter.
+
+**Syntax**
+
+```sql
+mapKeys(map)
+```
+
+**Parameters**
+
+-   `map`- Map.
+
+**Returned value**
+
+-   Array containing all the values from `map`.
+
+Type: [Array](../../sql-reference/data-types/array.md).
+
+**Example**
+
+Query:
+
+```sql
+CREATE TABLE test (a Map(String,String)) ENGINE = Memory;
+
+INSERT INTO test VALUES ({'name':'eleven','age':'11'}), ({'number':'twelve','position':'6.0'});
+
+SELECT mapValues(a) FROM test;
+```
+
+Result:
+
+```text
+┌─mapValues(a)─────┐
+│ ['eleven','11']  │
+│ ['twelve','6.0'] │
+└──────────────────┘
+```
+
 [Original article](https://clickhouse.tech/docs/en/query_language/functions/tuple-map-functions/) <!--hide-->

From 8b4d9e421a1037f132f8c6511b92ee1a3a21580b Mon Sep 17 00:00:00 2001
From: George <gyuton@yandex-team.ru>
Date: Thu, 11 Feb 2021 12:21:59 +0300
Subject: [PATCH 03/19] Added translation

---
 .../functions/tuple-map-functions.md          |   4 +-
 .../functions/tuple-map-functions.md          | 127 +++++++++++++++++-
 2 files changed, 128 insertions(+), 3 deletions(-)

diff --git a/docs/en/sql-reference/functions/tuple-map-functions.md b/docs/en/sql-reference/functions/tuple-map-functions.md
index d3503937af2..a08ca70e851 100644
--- a/docs/en/sql-reference/functions/tuple-map-functions.md
+++ b/docs/en/sql-reference/functions/tuple-map-functions.md
@@ -124,7 +124,7 @@ mapContains(map, key)
 
 **Parameters** 
 
--   `map` — Map. [Type name](relative/path/to/type/dscr.md#type).
+-   `map` — Map. 
 -   `key` — Key. Type matches the type of `map.keys`.
 
 **Returned value**
@@ -237,4 +237,4 @@ Result:
 └──────────────────┘
 ```
 
-[Original article](https://clickhouse.tech/docs/en/query_language/functions/tuple-map-functions/) <!--hide-->
+[Original article](https://clickhouse.tech/docs/en/sql-reference/functions/tuple-map-functions/) <!--hide-->
diff --git a/docs/ru/sql-reference/functions/tuple-map-functions.md b/docs/ru/sql-reference/functions/tuple-map-functions.md
index a2b25e68fe5..6461412aec5 100644
--- a/docs/ru/sql-reference/functions/tuple-map-functions.md
+++ b/docs/ru/sql-reference/functions/tuple-map-functions.md
@@ -116,4 +116,129 @@ select mapPopulateSeries([1,2,4], [11,22,44], 5) as res, toTypeName(res) as type
 └──────────────────────────────┴───────────────────────────────────┘
 ```
 
-[Оригинальная статья](https://clickhouse.tech/docs/en/query_language/functions/tuple-map-functions/) <!--hide-->
+## mapContains {#mapcontains}
+
+Определяет, включает ли в себя `map.keys` параметр `key`.
+
+**Синтаксис**
+
+``` sql
+mapContains(map, key)
+```
+
+**Параметры** 
+
+-   `map` — Map. 
+-   `key` — ключ. Тип соответстует типу `map.keys`.
+
+**Возвращаемое значение**
+
+-   `1` если `map.keys` включает `key`, иначе `0`.
+
+Тип: [UInt8](../../sql-reference/data-types/int-uint.md).
+
+**Пример**
+
+Запрос:
+
+```sql
+CREATE TABLE test (a Map(String,String)) ENGINE = Memory;
+
+INSERT INTO test VALUES ({'name':'eleven','age':'11'}), ({'number':'twelve','position':'6.0'});
+
+SELECT mapContains(a, 'name') FROM test;
+
+```
+
+Результат:
+
+```text
+┌─mapContains(a, 'name')─┐
+│                      1 │
+│                      0 │
+└────────────────────────┘
+```
+
+## mapKeys {#mapkeys}
+
+Возвращает все ключи контейнера `map`.
+
+**Синтаксис**
+
+```sql
+mapKeys(map)
+```
+
+**Параметры**
+
+-   `map`- map.
+
+**Возвращаемое значение**
+
+-   Массив со всеми ключами  контейнера `map`.
+
+Тип: [Array](../../sql-reference/data-types/array.md).
+
+**Пример**
+
+Запрос:
+
+```sql
+CREATE TABLE test (a Map(String,String)) ENGINE = Memory;
+
+INSERT INTO test VALUES ({'name':'eleven','age':'11'}), ({'number':'twelve','position':'6.0'});
+
+SELECT mapKeys(a) FROM test;
+```
+
+Результат:
+
+```text
+┌─mapKeys(a)────────────┐
+│ ['name','age']        │
+│ ['number','position'] │
+└───────────────────────┘
+```
+
+## mapValues {#mapvalues}
+
+Возвращает все значения контейнера `map`.
+
+**Синтаксис**
+
+```sql
+mapKeys(map)
+```
+
+**Параметры**
+
+-   `map`- map.
+
+**Возвращаемое значение**
+
+-   Массив со всеми значениями `map`.
+
+Тип: [Array](../../sql-reference/data-types/array.md).
+
+**Примеры**
+
+Запрос:
+
+```sql
+CREATE TABLE test (a Map(String,String)) ENGINE = Memory;
+
+INSERT INTO test VALUES ({'name':'eleven','age':'11'}), ({'number':'twelve','position':'6.0'});
+
+SELECT mapValues(a) FROM test;
+```
+
+Результат:
+
+```text
+┌─mapValues(a)─────┐
+│ ['eleven','11']  │
+│ ['twelve','6.0'] │
+└──────────────────┘
+```
+
+[Оригинальная статья](https://clickhouse.tech/docs/ru/sql-reference/functions/tuple-map-functions/) <!--hide-->

From 48b8685d6ef0e690ee7055f0ba1812fa8dfa50e1 Mon Sep 17 00:00:00 2001
From: George <gyuton@yandex-team.ru>
Date: Thu, 11 Feb 2021 12:46:14 +0300
Subject: [PATCH 04/19] minor fixes

---
 docs/en/sql-reference/functions/tuple-map-functions.md | 4 ++--
 docs/ru/sql-reference/functions/tuple-map-functions.md | 6 +++---
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/docs/en/sql-reference/functions/tuple-map-functions.md b/docs/en/sql-reference/functions/tuple-map-functions.md
index a08ca70e851..f8755f1e2a9 100644
--- a/docs/en/sql-reference/functions/tuple-map-functions.md
+++ b/docs/en/sql-reference/functions/tuple-map-functions.md
@@ -167,7 +167,7 @@ mapKeys(map)
 
 **Parameters**
 
--   `map`- Map.
+-   `map` — Map.
 
 **Returned value**
 
@@ -208,7 +208,7 @@ mapKeys(map)
 
 **Parameters**
 
--   `map`- Map.
+-   `map` — Map.
 
 **Returned value**
 
diff --git a/docs/ru/sql-reference/functions/tuple-map-functions.md b/docs/ru/sql-reference/functions/tuple-map-functions.md
index 6461412aec5..22bf1e98369 100644
--- a/docs/ru/sql-reference/functions/tuple-map-functions.md
+++ b/docs/ru/sql-reference/functions/tuple-map-functions.md
@@ -128,7 +128,7 @@ mapContains(map, key)
 
 **Параметры** 
 
--   `map` — Map. 
+-   `map` — контейнер map. 
 -   `key` — ключ. Тип соответстует типу `map.keys`.
 
 **Возвращаемое значение**
@@ -171,7 +171,7 @@ mapKeys(map)
 
 **Параметры**
 
--   `map`- map.
+-   `map` — контейнер map.
 
 **Возвращаемое значение**
 
@@ -212,7 +212,7 @@ mapKeys(map)
 
 **Параметры**
 
--   `map`- map.
+-   `map` — контейнер map.
 
 **Возвращаемое значение**
 

From cfb0dbb9e5f069342fe096542d888cbb2a01bc02 Mon Sep 17 00:00:00 2001
From: George <gyuton@yandex-team.ru>
Date: Sun, 21 Feb 2021 15:01:10 +0300
Subject: [PATCH 05/19] updated and added links

---
 .../functions/tuple-map-functions.md           | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/docs/en/sql-reference/functions/tuple-map-functions.md b/docs/en/sql-reference/functions/tuple-map-functions.md
index f8755f1e2a9..ac8d92750fd 100644
--- a/docs/en/sql-reference/functions/tuple-map-functions.md
+++ b/docs/en/sql-reference/functions/tuple-map-functions.md
@@ -114,7 +114,7 @@ Result:
 
 ## mapContains {#mapcontains}
 
-Determines  whether `map.keys` contains the `key` parameter.
+Determines  whether the `map` contains the `key` parameter.
 
 **Syntax**
 
@@ -124,12 +124,12 @@ mapContains(map, key)
 
 **Parameters** 
 
--   `map` — Map. 
--   `key` — Key. Type matches the type of `map.keys`.
+-   `map` — Map. [Map](../../sql-reference/data-types/map.md).
+-   `key` — Key. Type matches the type of `key` parameter.
 
 **Returned value**
 
--   `1` if `map.keys` contains `key`, `0` if not.
+-   `1` if `map` contains `key`, `0` if not.
 
 Type: [UInt8](../../sql-reference/data-types/int-uint.md).
 
@@ -157,7 +157,7 @@ Result:
 
 ## mapKeys {#mapkeys}
 
-Returns all the keys from `map` parameter.
+Returns all keys from the `map` parameter.
 
 **Syntax**
 
@@ -167,11 +167,11 @@ mapKeys(map)
 
 **Parameters**
 
--   `map` — Map.
+-   `map` — Map. [Map](../../sql-reference/data-types/map.md).
 
 **Returned value**
 
--   Array containing all the keys from `map`.
+-   Array containing all keys from the `map`.
 
 Type: [Array](../../sql-reference/data-types/array.md).
 
@@ -198,7 +198,7 @@ Result:
 
 ## mapValues {#mapvalues}
 
-Returns all the values from `map` parameter.
+Returns all values from the `map` parameter.
 
 **Syntax**
 
@@ -208,7 +208,7 @@ mapKeys(map)
 
 **Parameters**
 
--   `map` — Map.
+-   `map` — Map. [Map](../../sql-reference/data-types/map.md).
 
 **Returned value**
 

From bff08e32bfb00e1e73be8ab23c8f1263dc8ab455 Mon Sep 17 00:00:00 2001
From: George <gyuton@yandex-team.ru>
Date: Sun, 21 Feb 2021 15:22:48 +0300
Subject: [PATCH 06/19] updates

---
 .../sql-reference/functions/tuple-map-functions.md   |  2 +-
 .../sql-reference/functions/tuple-map-functions.md   | 12 ++++++------
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/docs/en/sql-reference/functions/tuple-map-functions.md b/docs/en/sql-reference/functions/tuple-map-functions.md
index 8bc36d19ed7..1d4839cbbf9 100644
--- a/docs/en/sql-reference/functions/tuple-map-functions.md
+++ b/docs/en/sql-reference/functions/tuple-map-functions.md
@@ -187,7 +187,7 @@ mapContains(map, key)
 **Parameters** 
 
 -   `map` — Map. [Map](../../sql-reference/data-types/map.md).
--   `key` — Key. Type matches the type of `key` parameter.
+-   `key` — Key. Type matches the type of keys of `map` parameter.
 
 **Returned value**
 
diff --git a/docs/ru/sql-reference/functions/tuple-map-functions.md b/docs/ru/sql-reference/functions/tuple-map-functions.md
index 7c69f2ca4ef..9516deb243a 100644
--- a/docs/ru/sql-reference/functions/tuple-map-functions.md
+++ b/docs/ru/sql-reference/functions/tuple-map-functions.md
@@ -178,7 +178,7 @@ select mapPopulateSeries([1,2,4], [11,22,44], 5) as res, toTypeName(res) as type
 
 ## mapContains {#mapcontains}
 
-Определяет, включает ли в себя `map.keys` параметр `key`.
+Определяет, включает ли в себя `map` параметр `key`.
 
 **Синтаксис**
 
@@ -188,12 +188,12 @@ mapContains(map, key)
 
 **Параметры** 
 
--   `map` — контейнер map. 
--   `key` — ключ. Тип соответстует типу `map.keys`.
+-   `map` — контейнер Map. [Map](../../sql-reference/data-types/map.md).
+-   `key` — ключ. Тип соответстует типу ключей параметра  `map`.
 
 **Возвращаемое значение**
 
--   `1` если `map.keys` включает `key`, иначе `0`.
+-   `1` если `map` включает `key`, иначе `0`.
 
 Тип: [UInt8](../../sql-reference/data-types/int-uint.md).
 
@@ -231,7 +231,7 @@ mapKeys(map)
 
 **Параметры**
 
--   `map` — контейнер map.
+-   `map` — контейнер Map. [Map](../../sql-reference/data-types/map.md).
 
 **Возвращаемое значение**
 
@@ -272,7 +272,7 @@ mapKeys(map)
 
 **Параметры**
 
--   `map` — контейнер map.
+-   `map` — контейнер Map. [Map](../../sql-reference/data-types/map.md).
 
 **Возвращаемое значение**
 

From 07e4cbcc06a2738cbad0be5fa46a1e15589352fa Mon Sep 17 00:00:00 2001
From: gyuton <40863448+gyuton@users.noreply.github.com>
Date: Tue, 23 Feb 2021 15:08:29 +0300
Subject: [PATCH 07/19] Update
 docs/ru/sql-reference/functions/tuple-map-functions.md

Co-authored-by: olgarev <56617294+olgarev@users.noreply.github.com>
---
 docs/ru/sql-reference/functions/tuple-map-functions.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/ru/sql-reference/functions/tuple-map-functions.md b/docs/ru/sql-reference/functions/tuple-map-functions.md
index 9516deb243a..e33fc83e67e 100644
--- a/docs/ru/sql-reference/functions/tuple-map-functions.md
+++ b/docs/ru/sql-reference/functions/tuple-map-functions.md
@@ -276,7 +276,7 @@ mapKeys(map)
 
 **Возвращаемое значение**
 
--   Массив со всеми значениями `map`.
+-   Массив со всеми значениями контейнера `map`.
 
 Тип: [Array](../../sql-reference/data-types/array.md).
 

From c223a87658088754de9791e8344b644e1b749752 Mon Sep 17 00:00:00 2001
From: gyuton <40863448+gyuton@users.noreply.github.com>
Date: Tue, 23 Feb 2021 15:08:34 +0300
Subject: [PATCH 08/19] Update
 docs/ru/sql-reference/functions/tuple-map-functions.md

Co-authored-by: olgarev <56617294+olgarev@users.noreply.github.com>
---
 docs/ru/sql-reference/functions/tuple-map-functions.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/ru/sql-reference/functions/tuple-map-functions.md b/docs/ru/sql-reference/functions/tuple-map-functions.md
index e33fc83e67e..52a6a972f75 100644
--- a/docs/ru/sql-reference/functions/tuple-map-functions.md
+++ b/docs/ru/sql-reference/functions/tuple-map-functions.md
@@ -178,7 +178,7 @@ select mapPopulateSeries([1,2,4], [11,22,44], 5) as res, toTypeName(res) as type
 
 ## mapContains {#mapcontains}
 
-Определяет, включает ли в себя `map` параметр `key`.
+Определяет, содержит ли контейнер `map` ключ `key`.
 
 **Синтаксис**
 

From 9f169aa13e415c8a040f8e0e282ec0b972543669 Mon Sep 17 00:00:00 2001
From: gyuton <40863448+gyuton@users.noreply.github.com>
Date: Tue, 23 Feb 2021 15:08:39 +0300
Subject: [PATCH 09/19] Update
 docs/ru/sql-reference/functions/tuple-map-functions.md

Co-authored-by: olgarev <56617294+olgarev@users.noreply.github.com>
---
 docs/ru/sql-reference/functions/tuple-map-functions.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/ru/sql-reference/functions/tuple-map-functions.md b/docs/ru/sql-reference/functions/tuple-map-functions.md
index 52a6a972f75..696fdb9e5ae 100644
--- a/docs/ru/sql-reference/functions/tuple-map-functions.md
+++ b/docs/ru/sql-reference/functions/tuple-map-functions.md
@@ -235,7 +235,7 @@ mapKeys(map)
 
 **Возвращаемое значение**
 
--   Массив со всеми ключами  контейнера `map`.
+-   Массив со всеми ключами контейнера `map`.
 
 Тип: [Array](../../sql-reference/data-types/array.md).
 

From a48bb7e3a01b42fd1e5b4fda7452fe0d73593b96 Mon Sep 17 00:00:00 2001
From: alesapin <alesapin@gmail.com>
Date: Fri, 26 Feb 2021 22:05:25 +0300
Subject: [PATCH 10/19] Fix redundant zookeeper reconnect and possibility of
 multiple zookeeper session for a single ClickHouse server

---
 docker/test/integration/base/Dockerfile       |  3 +-
 src/Common/ZooKeeper/IKeeper.h                |  3 ++
 src/Common/ZooKeeper/TestKeeper.h             |  2 +-
 src/Common/ZooKeeper/ZooKeeper.cpp            | 50 ++++++++++---------
 src/Common/ZooKeeper/ZooKeeper.h              | 15 ++++--
 src/Common/ZooKeeper/ZooKeeperImpl.h          |  2 +
 src/Interpreters/Context.cpp                  |  5 ++
 .../integration/test_reload_zookeeper/test.py |  8 +++
 8 files changed, 60 insertions(+), 28 deletions(-)

diff --git a/docker/test/integration/base/Dockerfile b/docker/test/integration/base/Dockerfile
index 4963ff0094d..938d8d45ffd 100644
--- a/docker/test/integration/base/Dockerfile
+++ b/docker/test/integration/base/Dockerfile
@@ -18,7 +18,8 @@ RUN apt-get update \
         curl \
         tar \
         krb5-user \
-        iproute2
+        iproute2 \
+        lsof
 RUN rm -rf \
         /var/lib/apt/lists/* \
         /var/cache/debconf \
diff --git a/src/Common/ZooKeeper/IKeeper.h b/src/Common/ZooKeeper/IKeeper.h
index c53ea60ec7c..9ff37a7045d 100644
--- a/src/Common/ZooKeeper/IKeeper.h
+++ b/src/Common/ZooKeeper/IKeeper.h
@@ -391,6 +391,9 @@ public:
     virtual void multi(
         const Requests & requests,
         MultiCallback callback) = 0;
+
+    /// Expire session and finish all pending requests
+    virtual void finalize() = 0;
 };
 
 }
diff --git a/src/Common/ZooKeeper/TestKeeper.h b/src/Common/ZooKeeper/TestKeeper.h
index ca9f584304f..a64b76336d2 100644
--- a/src/Common/ZooKeeper/TestKeeper.h
+++ b/src/Common/ZooKeeper/TestKeeper.h
@@ -83,6 +83,7 @@ public:
             const Requests & requests,
             MultiCallback callback) override;
 
+    void finalize() override;
 
     struct Node
     {
@@ -130,7 +131,6 @@ private:
 
     void pushRequest(RequestInfo && request);
 
-    void finalize();
 
     ThreadFromGlobalPool processing_thread;
 
diff --git a/src/Common/ZooKeeper/ZooKeeper.cpp b/src/Common/ZooKeeper/ZooKeeper.cpp
index a1c6eb9b481..599980a867a 100644
--- a/src/Common/ZooKeeper/ZooKeeper.cpp
+++ b/src/Common/ZooKeeper/ZooKeeper.cpp
@@ -44,7 +44,7 @@ static void check(Coordination::Error code, const std::string & path)
 }
 
 
-void ZooKeeper::init(const std::string & implementation_, const std::string & hosts_, const std::string & identity_,
+void ZooKeeper::init(const std::string & implementation_, const Strings & hosts_, const std::string & identity_,
                      int32_t session_timeout_ms_, int32_t operation_timeout_ms_, const std::string & chroot_)
 {
     log = &Poco::Logger::get("ZooKeeper");
@@ -60,13 +60,16 @@ void ZooKeeper::init(const std::string & implementation_, const std::string & ho
         if (hosts.empty())
             throw KeeperException("No hosts passed to ZooKeeper constructor.", Coordination::Error::ZBADARGUMENTS);
 
-        std::vector<std::string> hosts_strings;
-        splitInto<','>(hosts_strings, hosts);
         Coordination::ZooKeeper::Nodes nodes;
-        nodes.reserve(hosts_strings.size());
+        nodes.reserve(hosts.size());
+
+        Strings shuffled_hosts = hosts;
+        /// Shuffle the hosts to distribute the load among ZooKeeper nodes.
+        pcg64 generator(randomSeed());
+        std::shuffle(shuffled_hosts.begin(), shuffled_hosts.end(), generator);
 
         bool dns_error = false;
-        for (auto & host_string : hosts_strings)
+        for (auto & host_string : shuffled_hosts)
         {
             try
             {
@@ -109,9 +112,9 @@ void ZooKeeper::init(const std::string & implementation_, const std::string & ho
                 Poco::Timespan(0, operation_timeout_ms_ * 1000));
 
         if (chroot.empty())
-            LOG_TRACE(log, "Initialized, hosts: {}", hosts);
+            LOG_TRACE(log, "Initialized, hosts: {}", fmt::join(hosts, ","));
         else
-            LOG_TRACE(log, "Initialized, hosts: {}, chroot: {}", hosts, chroot);
+            LOG_TRACE(log, "Initialized, hosts: {}, chroot: {}", fmt::join(hosts, ","), chroot);
     }
     else if (implementation == "testkeeper")
     {
@@ -128,7 +131,16 @@ void ZooKeeper::init(const std::string & implementation_, const std::string & ho
         throw KeeperException("Zookeeper root doesn't exist. You should create root node " + chroot + " before start.", Coordination::Error::ZNONODE);
 }
 
-ZooKeeper::ZooKeeper(const std::string & hosts_, const std::string & identity_, int32_t session_timeout_ms_,
+ZooKeeper::ZooKeeper(const std::string & hosts_string, const std::string & identity_, int32_t session_timeout_ms_,
+                     int32_t operation_timeout_ms_, const std::string & chroot_, const std::string & implementation_)
+{
+    Strings hosts_;
+    splitInto<','>(hosts_, hosts_string);
+
+    init(implementation_, hosts_, identity_, session_timeout_ms_, operation_timeout_ms_, chroot_);
+}
+
+ZooKeeper::ZooKeeper(const Strings & hosts_, const std::string & identity_, int32_t session_timeout_ms_,
                      int32_t operation_timeout_ms_, const std::string & chroot_, const std::string & implementation_)
 {
     init(implementation_, hosts_, identity_, session_timeout_ms_, operation_timeout_ms_, chroot_);
@@ -141,8 +153,6 @@ struct ZooKeeperArgs
         Poco::Util::AbstractConfiguration::Keys keys;
         config.keys(config_name, keys);
 
-        std::vector<std::string> hosts_strings;
-
         session_timeout_ms = Coordination::DEFAULT_SESSION_TIMEOUT_MS;
         operation_timeout_ms = Coordination::DEFAULT_OPERATION_TIMEOUT_MS;
         implementation = "zookeeper";
@@ -150,7 +160,7 @@ struct ZooKeeperArgs
         {
             if (startsWith(key, "node"))
             {
-                hosts_strings.push_back(
+                hosts.push_back(
                         (config.getBool(config_name + "." + key + ".secure", false) ? "secure://" : "") +
                         config.getString(config_name + "." + key + ".host") + ":"
                         + config.getString(config_name + "." + key + ".port", "2181")
@@ -180,17 +190,6 @@ struct ZooKeeperArgs
                 throw KeeperException(std::string("Unknown key ") + key + " in config file", Coordination::Error::ZBADARGUMENTS);
         }
 
-        /// Shuffle the hosts to distribute the load among ZooKeeper nodes.
-        pcg64 generator(randomSeed());
-        std::shuffle(hosts_strings.begin(), hosts_strings.end(), generator);
-
-        for (auto & host : hosts_strings)
-        {
-            if (!hosts.empty())
-                hosts += ',';
-            hosts += host;
-        }
-
         if (!chroot.empty())
         {
             if (chroot.front() != '/')
@@ -200,7 +199,7 @@ struct ZooKeeperArgs
         }
     }
 
-    std::string hosts;
+    Strings hosts;
     std::string identity;
     int session_timeout_ms;
     int operation_timeout_ms;
@@ -922,6 +921,10 @@ Coordination::Error ZooKeeper::tryMultiNoThrow(const Coordination::Requests & re
     }
 }
 
+void ZooKeeper::finalize()
+{
+    impl->finalize();
+}
 
 size_t KeeperMultiException::getFailedOpIndex(Coordination::Error exception_code, const Coordination::Responses & responses)
 {
@@ -1000,4 +1003,5 @@ Coordination::RequestPtr makeCheckRequest(const std::string & path, int version)
     request->version = version;
     return request;
 }
+
 }
diff --git a/src/Common/ZooKeeper/ZooKeeper.h b/src/Common/ZooKeeper/ZooKeeper.h
index 5b37e4d6024..4a65ff070f7 100644
--- a/src/Common/ZooKeeper/ZooKeeper.h
+++ b/src/Common/ZooKeeper/ZooKeeper.h
@@ -50,7 +50,14 @@ class ZooKeeper
 public:
     using Ptr = std::shared_ptr<ZooKeeper>;
 
-    ZooKeeper(const std::string & hosts_, const std::string & identity_ = "",
+    /// hosts_string -- comma separated [secure://]host:port list
+    ZooKeeper(const std::string & hosts_string, const std::string & identity_ = "",
+              int32_t session_timeout_ms_ = Coordination::DEFAULT_SESSION_TIMEOUT_MS,
+              int32_t operation_timeout_ms_ = Coordination::DEFAULT_OPERATION_TIMEOUT_MS,
+              const std::string & chroot_ = "",
+              const std::string & implementation_ = "zookeeper");
+
+    ZooKeeper(const Strings & hosts_, const std::string & identity_ = "",
               int32_t session_timeout_ms_ = Coordination::DEFAULT_SESSION_TIMEOUT_MS,
               int32_t operation_timeout_ms_ = Coordination::DEFAULT_OPERATION_TIMEOUT_MS,
               const std::string & chroot_ = "",
@@ -247,10 +254,12 @@ public:
     /// Like the previous one but don't throw any exceptions on future.get()
     FutureMulti tryAsyncMulti(const Coordination::Requests & ops);
 
+    void finalize();
+
 private:
     friend class EphemeralNodeHolder;
 
-    void init(const std::string & implementation_, const std::string & hosts_, const std::string & identity_,
+    void init(const std::string & implementation_, const Strings & hosts_, const std::string & identity_,
               int32_t session_timeout_ms_, int32_t operation_timeout_ms_, const std::string & chroot_);
 
     /// The following methods don't throw exceptions but return error codes.
@@ -266,7 +275,7 @@ private:
 
     std::unique_ptr<Coordination::IKeeper> impl;
 
-    std::string hosts;
+    Strings hosts;
     std::string identity;
     int32_t session_timeout_ms;
     int32_t operation_timeout_ms;
diff --git a/src/Common/ZooKeeper/ZooKeeperImpl.h b/src/Common/ZooKeeper/ZooKeeperImpl.h
index 71b7cd56149..d8b9e23ced2 100644
--- a/src/Common/ZooKeeper/ZooKeeperImpl.h
+++ b/src/Common/ZooKeeper/ZooKeeperImpl.h
@@ -167,6 +167,8 @@ public:
         const Requests & requests,
         MultiCallback callback) override;
 
+    void finalize()  override { finalize(false, false); }
+
 private:
     String root_path;
     ACLs default_acls;
diff --git a/src/Interpreters/Context.cpp b/src/Interpreters/Context.cpp
index 98e4a87fba3..6f27a6bdb7d 100644
--- a/src/Interpreters/Context.cpp
+++ b/src/Interpreters/Context.cpp
@@ -1661,7 +1661,12 @@ void Context::resetZooKeeper() const
 static void reloadZooKeeperIfChangedImpl(const ConfigurationPtr & config, const std::string & config_name, zkutil::ZooKeeperPtr & zk)
 {
     if (!zk || zk->configChanged(*config, config_name))
+    {
+        if (zk)
+            zk->finalize();
+
         zk = std::make_shared<zkutil::ZooKeeper>(*config, config_name);
+    }
 }
 
 void Context::reloadZooKeeperIfChanged(const ConfigurationPtr & config) const
diff --git a/tests/integration/test_reload_zookeeper/test.py b/tests/integration/test_reload_zookeeper/test.py
index 82c47f4ec9e..1fe0ab13a7f 100644
--- a/tests/integration/test_reload_zookeeper/test.py
+++ b/tests/integration/test_reload_zookeeper/test.py
@@ -74,6 +74,9 @@ def test_reload_zookeeper(start_cluster):
     with pytest.raises(QueryRuntimeException):
         node.query("SELECT COUNT() FROM test_table", settings={"select_sequential_consistency" : 1})
 
+    def get_active_zk_connections():
+        return str(node.exec_in_container(['bash', '-c', 'lsof -a -i4 -i6 -itcp -w | grep 2181 | grep ESTABLISHED | wc -l'], privileged=True, user='root')).strip()
+
     ## set config to zoo2, server will be normal
     new_config = """
 <yandex>
@@ -89,5 +92,10 @@ def test_reload_zookeeper(start_cluster):
     node.replace_config("/etc/clickhouse-server/conf.d/zookeeper.xml", new_config)
     node.query("SYSTEM RELOAD CONFIG")
 
+    active_zk_connections = get_active_zk_connections()
+    assert active_zk_connections == '1', "Total connections to ZooKeeper not equal to 1, {}".format(active_zk_connections)
+
     assert_eq_with_retry(node, "SELECT COUNT() FROM test_table", '1000', retry_count=120, sleep_time=0.5)
 
+    active_zk_connections = get_active_zk_connections()
+    assert active_zk_connections == '1', "Total connections to ZooKeeper not equal to 1, {}".format(active_zk_connections)

From df95411d515500f3a15ba70f237febfe4aa2eb2f Mon Sep 17 00:00:00 2001
From: Sina <30809018+Sin4wd@users.noreply.github.com>
Date: Sat, 27 Feb 2021 01:04:35 +0330
Subject: [PATCH 11/19] Fix broken links in "See Also"

The link was transformed into "https://clickhouse.tech/docs/en/sql-reference/sql-reference/statements/create/table#ttl-expression" which did not exist and got 404.
---
 docs/en/sql-reference/statements/alter/ttl.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/docs/en/sql-reference/statements/alter/ttl.md b/docs/en/sql-reference/statements/alter/ttl.md
index 5331afdb2f8..e8bfb78ec68 100644
--- a/docs/en/sql-reference/statements/alter/ttl.md
+++ b/docs/en/sql-reference/statements/alter/ttl.md
@@ -81,5 +81,5 @@ The `TTL` is no longer there, so the second row is not deleted:
 
 ### See Also
 
-- More about the [TTL-expression](../../../sql-reference/statements/create/table#ttl-expression).
-- Modify column [with TTL](../../../sql-reference/statements/alter/column#alter_modify-column).
+- More about the [TTL-expression](../../../../sql-reference/statements/create/table#ttl-expression).
+- Modify column [with TTL](../../../../sql-reference/statements/alter/column#alter_modify-column).

From 9e93d7f507a61d747758e349fccc2b6b1057e528 Mon Sep 17 00:00:00 2001
From: alesapin <alesapin@gmail.com>
Date: Sat, 27 Feb 2021 11:07:14 +0300
Subject: [PATCH 12/19] Fix tidy and add comments

---
 src/Common/ZooKeeper/TestKeeper.h           |  2 +-
 src/Common/ZooKeeper/ZooKeeper.cpp          |  6 +++---
 src/Common/ZooKeeper/ZooKeeperImpl.h        | 14 +++++++++++++-
 src/Storages/StorageReplicatedMergeTree.cpp |  6 ++++++
 4 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/src/Common/ZooKeeper/TestKeeper.h b/src/Common/ZooKeeper/TestKeeper.h
index a64b76336d2..b46f98c0074 100644
--- a/src/Common/ZooKeeper/TestKeeper.h
+++ b/src/Common/ZooKeeper/TestKeeper.h
@@ -30,7 +30,7 @@ using TestKeeperRequestPtr = std::shared_ptr<TestKeeperRequest>;
   *
   * NOTE: You can add various failure modes for better testing.
   */
-class TestKeeper : public IKeeper
+class TestKeeper final : public IKeeper
 {
 public:
     TestKeeper(const String & root_path_, Poco::Timespan operation_timeout_);
diff --git a/src/Common/ZooKeeper/ZooKeeper.cpp b/src/Common/ZooKeeper/ZooKeeper.cpp
index 599980a867a..330985e1599 100644
--- a/src/Common/ZooKeeper/ZooKeeper.cpp
+++ b/src/Common/ZooKeeper/ZooKeeper.cpp
@@ -134,10 +134,10 @@ void ZooKeeper::init(const std::string & implementation_, const Strings & hosts_
 ZooKeeper::ZooKeeper(const std::string & hosts_string, const std::string & identity_, int32_t session_timeout_ms_,
                      int32_t operation_timeout_ms_, const std::string & chroot_, const std::string & implementation_)
 {
-    Strings hosts_;
-    splitInto<','>(hosts_, hosts_string);
+    Strings hosts_strings;
+    splitInto<','>(hosts_strings, hosts_string);
 
-    init(implementation_, hosts_, identity_, session_timeout_ms_, operation_timeout_ms_, chroot_);
+    init(implementation_, hosts_strings, identity_, session_timeout_ms_, operation_timeout_ms_, chroot_);
 }
 
 ZooKeeper::ZooKeeper(const Strings & hosts_, const std::string & identity_, int32_t session_timeout_ms_,
diff --git a/src/Common/ZooKeeper/ZooKeeperImpl.h b/src/Common/ZooKeeper/ZooKeeperImpl.h
index d8b9e23ced2..26d944814d8 100644
--- a/src/Common/ZooKeeper/ZooKeeperImpl.h
+++ b/src/Common/ZooKeeper/ZooKeeperImpl.h
@@ -88,7 +88,7 @@ using namespace DB;
 
 /** Usage scenario: look at the documentation for IKeeper class.
   */
-class ZooKeeper : public IKeeper
+class ZooKeeper final : public IKeeper
 {
 public:
     struct Node
@@ -167,6 +167,18 @@ public:
         const Requests & requests,
         MultiCallback callback) override;
 
+    /// Without forcefully invalidating (finalizing) ZooKeeper session before
+    /// establishing a new one, there was a possibility that server is using
+    /// two ZooKeeper sessions simultaneously in different parts of code.
+    /// This is stong antipattern and we always prevented it.
+
+    /// ZooKeeper is linearizeable for writes, but not linearizeable for
+    /// reads, it only maintains "sequential consistency": in every session
+    /// you observe all events in order but possibly with some delay. If you
+    /// perform write in one session, then notify different part of code and
+    /// it will do read in another session, that read may not see the
+    /// already performed write.
+
     void finalize()  override { finalize(false, false); }
 
 private:
diff --git a/src/Storages/StorageReplicatedMergeTree.cpp b/src/Storages/StorageReplicatedMergeTree.cpp
index f2c88cdedd9..94bf2dfcf6d 100644
--- a/src/Storages/StorageReplicatedMergeTree.cpp
+++ b/src/Storages/StorageReplicatedMergeTree.cpp
@@ -144,6 +144,12 @@ static const auto MUTATIONS_FINALIZING_IDLE_SLEEP_MS = 5 * 1000;
 
 void StorageReplicatedMergeTree::setZooKeeper()
 {
+    /// Every ReplicatedMergeTree table is using only one ZooKeeper session.
+    /// But if several ReplicatedMergeTree tables are using different
+    /// ZooKeeper sessions, some queries like ATTACH PARTITION FROM may have
+    /// strange effects. So we always use only one session for all tables.
+    /// (excluding auxiliary zookeepers)
+
     std::lock_guard lock(current_zookeeper_mutex);
     if (zookeeper_name == default_zookeeper_name)
     {

From 9dc3952ff35f17a5dddb9e50b02da615949a87c5 Mon Sep 17 00:00:00 2001
From: alesapin <alesapin@gmail.com>
Date: Sat, 27 Feb 2021 16:30:43 +0300
Subject: [PATCH 13/19] Fix typo

---
 src/Common/ZooKeeper/ZooKeeperImpl.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Common/ZooKeeper/ZooKeeperImpl.h b/src/Common/ZooKeeper/ZooKeeperImpl.h
index 26d944814d8..afd2e89538f 100644
--- a/src/Common/ZooKeeper/ZooKeeperImpl.h
+++ b/src/Common/ZooKeeper/ZooKeeperImpl.h
@@ -170,7 +170,7 @@ public:
     /// Without forcefully invalidating (finalizing) ZooKeeper session before
     /// establishing a new one, there was a possibility that server is using
     /// two ZooKeeper sessions simultaneously in different parts of code.
-    /// This is stong antipattern and we always prevented it.
+    /// This is strong antipattern and we always prevented it.
 
     /// ZooKeeper is linearizeable for writes, but not linearizeable for
     /// reads, it only maintains "sequential consistency": in every session

From 4f61ef3099f42f17b496a0b0424773978d9a32dc Mon Sep 17 00:00:00 2001
From: kssenii <sumarokovakseniia@mail.ru>
Date: Sat, 27 Feb 2021 08:49:45 +0000
Subject: [PATCH 14/19] Tests for zstd and zlib

---
 ...lib_http_compression_json_format.reference | 23 +++++++++++++++++++
 ..._long_zlib_http_compression_json_format.sh |  7 ++++++
 ...std_http_compression_json_format.reference | 23 +++++++++++++++++++
 ..._long_zstd_http_compression_json_format.sh |  7 ++++++
 4 files changed, 60 insertions(+)
 create mode 100644 tests/queries/0_stateless/01746_long_zlib_http_compression_json_format.reference
 create mode 100755 tests/queries/0_stateless/01746_long_zlib_http_compression_json_format.sh
 create mode 100644 tests/queries/0_stateless/01746_long_zstd_http_compression_json_format.reference
 create mode 100755 tests/queries/0_stateless/01746_long_zstd_http_compression_json_format.sh

diff --git a/tests/queries/0_stateless/01746_long_zlib_http_compression_json_format.reference b/tests/queries/0_stateless/01746_long_zlib_http_compression_json_format.reference
new file mode 100644
index 00000000000..7c089a2fd05
--- /dev/null
+++ b/tests/queries/0_stateless/01746_long_zlib_http_compression_json_format.reference
@@ -0,0 +1,23 @@
+		},
+		{
+			"datetime": "2020-12-12",
+			"pipeline": "test-pipeline",
+			"host": "clickhouse-test-host-001.clickhouse.com",
+			"home": "clickhouse",
+			"detail": "clickhouse",
+			"row_number": "999998"
+		},
+		{
+			"datetime": "2020-12-12",
+			"pipeline": "test-pipeline",
+			"host": "clickhouse-test-host-001.clickhouse.com",
+			"home": "clickhouse",
+			"detail": "clickhouse",
+			"row_number": "999999"
+		}
+	],
+
+	"rows": 1000000,
+
+	"rows_before_limit_at_least": 1048080,
+
diff --git a/tests/queries/0_stateless/01746_long_zlib_http_compression_json_format.sh b/tests/queries/0_stateless/01746_long_zlib_http_compression_json_format.sh
new file mode 100755
index 00000000000..e663b329660
--- /dev/null
+++ b/tests/queries/0_stateless/01746_long_zlib_http_compression_json_format.sh
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+CURDIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+# shellcheck source=../shell_config.sh
+. "$CURDIR"/../shell_config.sh
+
+${CLICKHOUSE_CURL} -sS -H 'Accept-Encoding: gzip'              "${CLICKHOUSE_URL}&enable_http_compression=1&http_zlib_compression_level=1" -d "SELECT toDate('2020-12-12') as datetime, 'test-pipeline' as pipeline, 'clickhouse-test-host-001.clickhouse.com' as host, 'clickhouse' as home, 'clickhouse' as detail, number as row_number FROM numbers(1000000) FORMAT JSON" | gzip -d | tail -n30 | head -n23
diff --git a/tests/queries/0_stateless/01746_long_zstd_http_compression_json_format.reference b/tests/queries/0_stateless/01746_long_zstd_http_compression_json_format.reference
new file mode 100644
index 00000000000..7c089a2fd05
--- /dev/null
+++ b/tests/queries/0_stateless/01746_long_zstd_http_compression_json_format.reference
@@ -0,0 +1,23 @@
+		},
+		{
+			"datetime": "2020-12-12",
+			"pipeline": "test-pipeline",
+			"host": "clickhouse-test-host-001.clickhouse.com",
+			"home": "clickhouse",
+			"detail": "clickhouse",
+			"row_number": "999998"
+		},
+		{
+			"datetime": "2020-12-12",
+			"pipeline": "test-pipeline",
+			"host": "clickhouse-test-host-001.clickhouse.com",
+			"home": "clickhouse",
+			"detail": "clickhouse",
+			"row_number": "999999"
+		}
+	],
+
+	"rows": 1000000,
+
+	"rows_before_limit_at_least": 1048080,
+
diff --git a/tests/queries/0_stateless/01746_long_zstd_http_compression_json_format.sh b/tests/queries/0_stateless/01746_long_zstd_http_compression_json_format.sh
new file mode 100755
index 00000000000..f520a21e9b3
--- /dev/null
+++ b/tests/queries/0_stateless/01746_long_zstd_http_compression_json_format.sh
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+CURDIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+# shellcheck source=../shell_config.sh
+. "$CURDIR"/../shell_config.sh
+
+${CLICKHOUSE_CURL} -sS -H 'Accept-Encoding: zstd'              "${CLICKHOUSE_URL}&enable_http_compression=1" -d "SELECT toDate('2020-12-12') as datetime, 'test-pipeline' as pipeline, 'clickhouse-test-host-001.clickhouse.com' as host, 'clickhouse' as home, 'clickhouse' as detail, number as row_number FROM numbers(1000000) FORMAT JSON" | zstd -d | tail -n30 | head -n23

From 2cafd54c17c75450bc3df9bc909e533621fe986e Mon Sep 17 00:00:00 2001
From: Alexey Milovidov <milovidov@yandex-team.ru>
Date: Sat, 27 Feb 2021 17:42:31 +0300
Subject: [PATCH 15/19] Add new dataset: Cell Towers

---
 .../example-datasets/cell-towers.md           | 133 ++++++++++++++++++
 .../getting-started/example-datasets/index.md |   1 +
 2 files changed, 134 insertions(+)
 create mode 100644 docs/en/getting-started/example-datasets/cell-towers.md

diff --git a/docs/en/getting-started/example-datasets/cell-towers.md b/docs/en/getting-started/example-datasets/cell-towers.md
new file mode 100644
index 00000000000..f032be76da0
--- /dev/null
+++ b/docs/en/getting-started/example-datasets/cell-towers.md
@@ -0,0 +1,133 @@
+---
+toc_priority: 21
+toc_title: Cell Stations
+---
+
+# Cell Stations
+
+This dataset is from [OpenCellid](https://www.opencellid.org/) - The world's largest Open Database of Cell Towers.
+
+As of 2021 it contains more than 40 million records about cell towers (GSM, LTE, UMTS, etc.) around the world with their geographical coordinates and metadata (country code, network, etc).
+
+OpenCelliD Project is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, and we redistribute a snapshot of this dataset under the terms of the same license. The up to date version of the dataset is available to download after sign in.
+
+
+## Get the Dataset
+
+Download the snapshot of the dataset from Feb 2021: [https://datasets.clickhouse.tech/cell_towers.csv.xz] (729 MB).
+
+Optionally validate the integrity:
+```
+md5sum cell_towers.csv.xz
+8cf986f4a0d9f12c6f384a0e9192c908  cell_towers.csv.xz
+```
+
+Decompress it with the following command:
+```
+xz -d cell_towers.csv.xz
+```
+
+Create a table:
+
+```
+CREATE TABLE cell_towers
+(
+    radio Enum8('' = 0, 'CDMA' = 1, 'GSM' = 2, 'LTE' = 3, 'NR' = 4, 'UMTS' = 5),
+    mcc UInt16,
+    net UInt16,
+    area UInt16,
+    cell UInt64,
+    unit Int16,
+    lon Float64,
+    lat Float64,
+    range UInt32,
+    samples UInt32,
+    changeable UInt8,
+    created DateTime,
+    updated DateTime,
+    averageSignal UInt8
+)
+ENGINE = MergeTree ORDER BY (radio, mcc, net, created);
+```
+
+Insert the dataset:
+```
+clickhouse-client --query "INSERT INTO cell_towers FORMAT CSVWithNames" < cell_towers.csv
+```
+
+
+## Run some queries
+
+Number of cell towers by type:
+```
+SELECT radio, count() AS c FROM cell_towers GROUP BY radio ORDER BY c DESC
+
+┌─radio─┬────────c─┐
+│ UMTS  │ 20686487 │
+│ LTE   │ 12101148 │
+│ GSM   │  9931312 │
+│ CDMA  │   556344 │
+│ NR    │      867 │
+└───────┴──────────┘
+
+5 rows in set. Elapsed: 0.011 sec. Processed 43.28 million rows, 43.28 MB (3.83 billion rows/s., 3.83 GB/s.)
+```
+
+Cell towers by mobile country code (MCC):
+```
+SELECT mcc, count() FROM cell_towers GROUP BY mcc ORDER BY count() DESC LIMIT 10
+
+┌─mcc─┬─count()─┐
+│ 310 │ 5024650 │
+│ 262 │ 2622423 │
+│ 250 │ 1953176 │
+│ 208 │ 1891187 │
+│ 724 │ 1836150 │
+│ 404 │ 1729151 │
+│ 234 │ 1618924 │
+│ 510 │ 1353998 │
+│ 440 │ 1343355 │
+│ 311 │ 1332798 │
+└─────┴─────────┘
+
+10 rows in set. Elapsed: 0.019 sec. Processed 43.28 million rows, 86.55 MB (2.33 billion rows/s., 4.65 GB/s.)
+```
+
+See the dictionary here: [https://en.wikipedia.org/wiki/Mobile_country_code](https://en.wikipedia.org/wiki/Mobile_country_code).
+
+So, the top countries are USA, Germany and Russia.
+
+You may want to create an [External Dictionary](../../sql-reference/dictionaries/external-dictionaries/external-dicts/) in ClickHouse to decode these values.
+
+
+### Example of using `pointInPolygon` function
+
+Create a table where we will store polygons:
+
+```
+CREATE TEMPORARY TABLE moscow (polygon Array(Tuple(Float64, Float64)));
+```
+
+This is a rough shape of Moscow (without "new Moscow"):
+
+```
+INSERT INTO moscow VALUES ([(37.84172564285271, 55.78000432402266), (37.8381207618713, 55.775874525970494), (37.83979446823122, 55.775626746008065), (37.84243326983639, 55.77446586811748), (37.84262672750849, 55.771974101091104), (37.84153238623039, 55.77114545193181), (37.841124690460184, 55.76722010265554), (37.84239076983644, 55.76654891107098), (37.842283558197025, 55.76258709833121), (37.8421759312134, 55.758073999993734), (37.84198330422974, 55.75381499999371), (37.8416827275085, 55.749277102484484), (37.84157576190186, 55.74794544108413), (37.83897929098507, 55.74525257875241), (37.83739676451868, 55.74404373042019), (37.838732481460525, 55.74298009816793), (37.841183997352545, 55.743060321833575), (37.84097476190185, 55.73938799999373), (37.84048155819702, 55.73570799999372), (37.840095812164286, 55.73228210777237), (37.83983814285274, 55.73080491981639), (37.83846476321406, 55.729799917464675), (37.83835745269769, 55.72919751082619), (37.838636380279524, 55.72859509486539), (37.8395161005249, 55.727705075632784), (37.83897964285276, 55.722727886185154), (37.83862557539366, 55.72034817326636), (37.83559735744853, 55.71944437307499), (37.835370708803126, 55.71831419154461), (37.83738169402022, 55.71765218986692), (37.83823396494291, 55.71691750159089), (37.838056931213345, 55.71547311301385), (37.836812846557606, 55.71221445615604), (37.83522525396725, 55.709331054395555), (37.83269301586908, 55.70953687463627), (37.829667367706236, 55.70903403789297), (37.83311126588435, 55.70552351822608), (37.83058993121339, 55.70041317726053), (37.82983872750851, 55.69883771404813), (37.82934501586913, 55.69718947487017), (37.828926414016685, 55.69504441658371), (37.82876530422971, 55.69287499999378), (37.82894754100031, 55.690759754047335), (37.827697554878185, 55.68951421135665), (37.82447346292115, 55.68965045405069), (37.83136543914793, 55.68322046195302), (37.833554015869154, 55.67814012759211), (37.83544184655761, 55.67295011628339), (37.837480388885474, 55.6672498719639), (37.838960677246064, 55.66316274139358), (37.83926093121332, 55.66046999999383), (37.839025050262435, 55.65869897264431), (37.83670784390257, 55.65794084879904), (37.835656529083245, 55.65694309303843), (37.83704060449217, 55.65689306460552), (37.83696819873806, 55.65550363526252), (37.83760389616388, 55.65487847246661), (37.83687972750851, 55.65356745541324), (37.83515216004943, 55.65155951234079), (37.83312418518067, 55.64979413590619), (37.82801726983639, 55.64640836412121), (37.820614174591, 55.64164525405531), (37.818908190475426, 55.6421883258084), (37.81717543386075, 55.64112490388471), (37.81690987037274, 55.63916106913107), (37.815099354492155, 55.637925371757085), (37.808769150787356, 55.633798276884455), (37.80100123544311, 55.62873670012244), (37.79598013491824, 55.62554336109055), (37.78634567724606, 55.62033499605651), (37.78334147619623, 55.618768681480326), (37.77746201055901, 55.619855533402706), (37.77527329626457, 55.61909966711279), (37.77801986242668, 55.618770300976294), (37.778212973541216, 55.617257701952106), (37.77784818518065, 55.61574504433011), (37.77016867724609, 55.61148576294007), (37.760191219573976, 55.60599579539028), (37.75338926983641, 55.60227892751446), (37.746329965606634, 55.59920577639331), (37.73939925396728, 55.59631430313617), (37.73273665739439, 55.5935318803559), (37.7299954450912, 55.59350760316188), (37.7268679946899, 55.59469840523759), (37.72626726983634, 55.59229549697373), (37.7262673598022, 55.59081598950582), (37.71897193121335, 55.5877595845419), (37.70871550793456, 55.58393177431724), (37.700497489410374, 55.580917323756644), (37.69204305026244, 55.57778089778455), (37.68544477378839, 55.57815154690915), (37.68391050793454, 55.57472945079756), (37.678803592590306, 55.57328235936491), (37.6743402539673, 55.57255251445782), (37.66813862698363, 55.57216388774464), (37.617927457672096, 55.57505691895805), (37.60443099999999, 55.5757737568051), (37.599683515869145, 55.57749105910326), (37.59754177842709, 55.57796291823627), (37.59625834786988, 55.57906686095235), (37.59501783265684, 55.57746616444403), (37.593090671936025, 55.57671634534502), (37.587018007904, 55.577944600233785), (37.578692203704804, 55.57982895000019), (37.57327546607398, 55.58116294118248), (37.57385012109279, 55.581550362779), (37.57399562266922, 55.5820107079112), (37.5735356072979, 55.58226289171689), (37.57290393054962, 55.582393529795155), (37.57037722355653, 55.581919415056234), (37.5592298306885, 55.584471614867844), (37.54189249206543, 55.58867650795186), (37.5297256269836, 55.59158133551745), (37.517837865081766, 55.59443656218868), (37.51200186508174, 55.59635625174229), (37.506808949737554, 55.59907823904434), (37.49820432275389, 55.6062944994944), (37.494406071441674, 55.60967103463367), (37.494760001358024, 55.61066689753365), (37.49397137107085, 55.61220931698269), (37.49016528606031, 55.613417718449064), (37.48773249206542, 55.61530616333343), (37.47921386508177, 55.622640129112334), (37.470652153442394, 55.62993723476164), (37.46273446298218, 55.6368075123157), (37.46350692265317, 55.64068225239439), (37.46050283203121, 55.640794546982576), (37.457627470916734, 55.64118904154646), (37.450718034393326, 55.64690488145138), (37.44239252645875, 55.65397824729769), (37.434587576721185, 55.66053543155961), (37.43582144975277, 55.661693766520735), (37.43576786245721, 55.662755031737014), (37.430982915344174, 55.664610641628116), (37.428547447097685, 55.66778515273695), (37.42945134592044, 55.668633314343566), (37.42859571562949, 55.66948145750025), (37.4262836402282, 55.670813882451405), (37.418709037048295, 55.6811141674414), (37.41922139651101, 55.68235377885389), (37.419218771842885, 55.68359335082235), (37.417196501327446, 55.684375235224735), (37.41607020370478, 55.68540557585352), (37.415640857147146, 55.68686637150793), (37.414632153442334, 55.68903015131686), (37.413344899475064, 55.690896881757396), (37.41171432275391, 55.69264232162232), (37.40948282275393, 55.69455101638112), (37.40703674603271, 55.69638690385348), (37.39607169577025, 55.70451821283731), (37.38952706878662, 55.70942491932811), (37.387778313491815, 55.71149057784176), (37.39049275399779, 55.71419814298992), (37.385557272491454, 55.7155489617061), (37.38388335714726, 55.71849856042102), (37.378368238098155, 55.7292763261685), (37.37763597123337, 55.730845879211614), (37.37890062088197, 55.73167906388319), (37.37750451918789, 55.734703664681774), (37.375610832015965, 55.734851959522246), (37.3723813571472, 55.74105626086403), (37.37014935714723, 55.746115620904355), (37.36944173016362, 55.750883999993725), (37.36975304365541, 55.76335905525834), (37.37244070571134, 55.76432079697595), (37.3724259757175, 55.76636979670426), (37.369922155757884, 55.76735417953104), (37.369892695770275, 55.76823419316575), (37.370214730163575, 55.782312184391266), (37.370493611114505, 55.78436801120489), (37.37120164550783, 55.78596427165359), (37.37284851456452, 55.7874378183096), (37.37608325135799, 55.7886695054807), (37.3764587460632, 55.78947647305964), (37.37530000265506, 55.79146512926804), (37.38235915344241, 55.79899647809345), (37.384344043655396, 55.80113596939471), (37.38594269577028, 55.80322699999366), (37.38711208598329, 55.804919036911976), (37.3880239841309, 55.806610999993666), (37.38928977249147, 55.81001864976979), (37.39038389947512, 55.81348641242801), (37.39235781481933, 55.81983538336746), (37.393709457672124, 55.82417822811877), (37.394685720901464, 55.82792275755836), (37.39557615344238, 55.830447148154136), (37.39844478226658, 55.83167107969975), (37.40019761214057, 55.83151823557964), (37.400398790382326, 55.83264967594742), (37.39659544313046, 55.83322180909622), (37.39667059524539, 55.83402792148566), (37.39682089947515, 55.83638877400216), (37.39643489154053, 55.83861656112751), (37.3955338994751, 55.84072348043264), (37.392680272491454, 55.84502158126453), (37.39241188227847, 55.84659117913199), (37.392529730163616, 55.84816071336481), (37.39486835714723, 55.85288092980303), (37.39873052645878, 55.859893456073635), (37.40272161111449, 55.86441833633205), (37.40697072750854, 55.867579567544375), (37.410007082016016, 55.868369880337), (37.4120992989502, 55.86920843741314), (37.412668021163924, 55.87055369615854), (37.41482461111453, 55.87170587948249), (37.41862266137694, 55.873183961039565), (37.42413732540892, 55.874879126654704), (37.4312182698669, 55.875614937236705), (37.43111093783558, 55.8762723478417), (37.43332105622856, 55.87706546369396), (37.43385747619623, 55.87790681284802), (37.441303050262405, 55.88027084462084), (37.44747234260555, 55.87942070143253), (37.44716141796871, 55.88072960917233), (37.44769797085568, 55.88121221323979), (37.45204320500181, 55.882080694420715), (37.45673176190186, 55.882346110794586), (37.463383999999984, 55.88252729504517), (37.46682797486874, 55.88294937719063), (37.470014457672086, 55.88361266759345), (37.47751410450743, 55.88546991372396), (37.47860317658232, 55.88534929207307), (37.48165826025772, 55.882563306475106), (37.48316434442331, 55.8815803226785), (37.483831555817645, 55.882427612793315), (37.483182967125686, 55.88372791409729), (37.483092277908824, 55.88495581062434), (37.4855716508179, 55.8875561994203), (37.486440636245746, 55.887827444039566), (37.49014203439328, 55.88897899871799), (37.493210285705544, 55.890208937135604), (37.497512451065035, 55.891342397444696), (37.49780744510645, 55.89174030252967), (37.49940333499519, 55.89239745507079), (37.50018383334346, 55.89339220941865), (37.52421672750851, 55.903869074155224), (37.52977457672118, 55.90564076517974), (37.53503220370484, 55.90661661218259), (37.54042858064267, 55.90714113744566), (37.54320461007303, 55.905645048442985), (37.545686966066306, 55.906608607018505), (37.54743976120755, 55.90788552162358), (37.55796999999999, 55.90901557907218), (37.572711542327866, 55.91059395704873), (37.57942799999998, 55.91073854155573), (37.58502865872187, 55.91009969268444), (37.58739968913264, 55.90794809960554), (37.59131567193598, 55.908713267595054), (37.612687423278814, 55.902866854295375), (37.62348079629517, 55.90041967242986), (37.635797880950896, 55.898141151686396), (37.649487626983664, 55.89639275532968), (37.65619302513125, 55.89572360207488), (37.66294133862307, 55.895295577183965), (37.66874564418033, 55.89505457604897), (37.67375601586915, 55.89254677027454), (37.67744661901856, 55.8947775867987), (37.688347, 55.89450045676125), (37.69480554232789, 55.89422926332761), (37.70107096560668, 55.89322256101114), (37.705962965606716, 55.891763491662616), (37.711885134918205, 55.889110234998974), (37.71682005026245, 55.886577568759876), (37.7199315476074, 55.88458159806678), (37.72234560316464, 55.882281005794134), (37.72364385977171, 55.8809452036196), (37.725371142837474, 55.8809722706006), (37.727870902099546, 55.88037213862385), (37.73394330422971, 55.877941504088696), (37.745339592590376, 55.87208120378722), (37.75525267724611, 55.86703807949492), (37.76919976190188, 55.859821640197474), (37.827835219574, 55.82962968399116), (37.83341438888553, 55.82575289922351), (37.83652584655761, 55.82188784027888), (37.83809213491821, 55.81612575504693), (37.83605359521481, 55.81460347077685), (37.83632178569025, 55.81276696067908), (37.838623105812026, 55.811486181656385), (37.83912198147584, 55.807329380532785), (37.839079078033414, 55.80510270463816), (37.83965844708251, 55.79940712529036), (37.840581150787344, 55.79131399999368), (37.84172564285271, 55.78000432402266)]);
+```
+
+Check how many cell towers are in Moscow:
+
+```
+SELECT count() FROM cell_towers WHERE pointInPolygon((lon, lat), (SELECT * FROM moscow))
+
+┌─count()─┐
+│  310463 │
+└─────────┘
+
+1 rows in set. Elapsed: 0.067 sec. Processed 43.28 million rows, 692.42 MB (645.83 million rows/s., 10.33 GB/s.)
+```
+
+The data is also available for interactive queries in the [Playground](https://gh-api.clickhouse.tech/play?user=play), [example](https://gh-api.clickhouse.tech/play?user=play#U0VMRUNUIG1jYywgY291bnQoKSBGUk9NIGNlbGxfdG93ZXJzIEdST1VQIEJZIG1jYyBPUkRFUiBCWSBjb3VudCgpIERFU0M=).
+
+Although you cannot create temporary tables there.
+
+[Original article](https://clickhouse.tech/docs/en/getting_started/example_datasets/cell-towers/) <!--hide-->
diff --git a/docs/en/getting-started/example-datasets/index.md b/docs/en/getting-started/example-datasets/index.md
index 72f44d8caf1..53007c33306 100644
--- a/docs/en/getting-started/example-datasets/index.md
+++ b/docs/en/getting-started/example-datasets/index.md
@@ -20,5 +20,6 @@ The list of documented datasets:
 -   [Terabyte of Click Logs from Criteo](../../getting-started/example-datasets/criteo.md)
 -   [AMPLab Big Data Benchmark](../../getting-started/example-datasets/amplab-benchmark.md)
 -   [Brown University Benchmark](../../getting-started/example-datasets/brown-benchmark.md)
+-   [Cell Towers](../../getting-started/example-datasets/cell-towers.md)
 
 [Original article](https://clickhouse.tech/docs/en/getting_started/example_datasets) <!--hide-->

From 5e3c9a5debedf927a789e75b8daed4d657d40e3d Mon Sep 17 00:00:00 2001
From: Alexey Milovidov <milovidov@yandex-team.ru>
Date: Sat, 27 Feb 2021 17:44:12 +0300
Subject: [PATCH 16/19] Rename

---
 docs/en/getting-started/example-datasets/cell-towers.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/docs/en/getting-started/example-datasets/cell-towers.md b/docs/en/getting-started/example-datasets/cell-towers.md
index f032be76da0..76effdd4c62 100644
--- a/docs/en/getting-started/example-datasets/cell-towers.md
+++ b/docs/en/getting-started/example-datasets/cell-towers.md
@@ -1,9 +1,9 @@
 ---
 toc_priority: 21
-toc_title: Cell Stations
+toc_title: Cell Towers
 ---
 
-# Cell Stations
+# Cell Towers
 
 This dataset is from [OpenCellid](https://www.opencellid.org/) - The world's largest Open Database of Cell Towers.
 

From 315824978de64164442ce8c5c6b5cb161041a72b Mon Sep 17 00:00:00 2001
From: Maksim Kita <maksim-kita@yandex-team.ru>
Date: Sat, 27 Feb 2021 19:19:21 +0300
Subject: [PATCH 17/19] CheckConstraintsBlockOutputStream optimize nullable
 column case

---
 src/DataStreams/CheckConstraintsBlockOutputStream.cpp | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/src/DataStreams/CheckConstraintsBlockOutputStream.cpp b/src/DataStreams/CheckConstraintsBlockOutputStream.cpp
index 90d6560b9a8..3b0b4db72f9 100644
--- a/src/DataStreams/CheckConstraintsBlockOutputStream.cpp
+++ b/src/DataStreams/CheckConstraintsBlockOutputStream.cpp
@@ -65,10 +65,8 @@ void CheckConstraintsBlockOutputStream::write(const Block & block)
 
                 /// Check if constraint value is nullable
                 const auto & null_map = column_nullable->getNullMapColumn();
-                const auto & data = null_map.getData();
-                const auto * it = std::find(data.begin(), data.end(), true);
-
-                bool null_map_contains_null = it != data.end();
+                const PaddedPODArray<UInt8> & data = null_map.getData();
+                bool null_map_contains_null = !memoryIsZero(data.raw_data(), data.size() * sizeof(UInt8));
 
                 if (null_map_contains_null)
                     throw Exception(

From bb5a8241b94739a3828bf98e041a6a489d32e7f9 Mon Sep 17 00:00:00 2001
From: Nikolay <211292+kolya7k@users.noreply.github.com>
Date: Sat, 27 Feb 2021 21:05:04 +0300
Subject: [PATCH 18/19] Add information about my ClickHouse PHP extension

I made a native PHP extension for ClickHouse using the clickhouse-cpp library.
My goal is to make a fast extension for ClickHouse with interface similar to mysqli.
---
 docs/ru/interfaces/third-party/client-libraries.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/docs/ru/interfaces/third-party/client-libraries.md b/docs/ru/interfaces/third-party/client-libraries.md
index 26e05b02509..97fa382fdd9 100644
--- a/docs/ru/interfaces/third-party/client-libraries.md
+++ b/docs/ru/interfaces/third-party/client-libraries.md
@@ -22,6 +22,7 @@ toc_title: "\u041a\u043b\u0438\u0435\u043d\u0442\u0441\u043a\u0438\u0435\u0020\u
     -   [seva-code/php-click-house-client](https://packagist.org/packages/seva-code/php-click-house-client)
     -   [SeasClick C++ client](https://github.com/SeasX/SeasClick)
     -   [glushkovds/phpclickhouse-laravel](https://packagist.org/packages/glushkovds/phpclickhouse-laravel)
+    -   [kolya7k ClickHouse PHP extension](https://github.com//kolya7k/clickhouse-php)
 -   Go
     -   [clickhouse](https://github.com/kshvakov/clickhouse/)
     -   [go-clickhouse](https://github.com/roistat/go-clickhouse)

From 01ef06a42c4c213a6ec0d0c9188ab10e5a2f07b9 Mon Sep 17 00:00:00 2001
From: Alexey Milovidov <milovidov@yandex-team.ru>
Date: Sun, 28 Feb 2021 02:31:47 +0300
Subject: [PATCH 19/19] Fix broken links

---
 docs/en/sql-reference/functions/hash-functions.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/docs/en/sql-reference/functions/hash-functions.md b/docs/en/sql-reference/functions/hash-functions.md
index 6bf1bebabaa..465ad01527f 100644
--- a/docs/en/sql-reference/functions/hash-functions.md
+++ b/docs/en/sql-reference/functions/hash-functions.md
@@ -9,7 +9,7 @@ Hash functions can be used for the deterministic pseudo-random shuffling of elem
 
 ## halfMD5 {#hash-functions-halfmd5}
 
-[Interprets](../../sql-reference/functions/type-conversion-functions.md#type_conversion_function-reinterpretAsString) all the input parameters as strings and calculates the [MD5](https://en.wikipedia.org/wiki/MD5) hash value for each of them. Then combines hashes, takes the first 8 bytes of the hash of the resulting string, and interprets them as `UInt64` in big-endian byte order.
+[Interprets](../../sql-reference/functions/type-conversion-functions.md#type_conversion_functions-reinterpretAsString) all the input parameters as strings and calculates the [MD5](https://en.wikipedia.org/wiki/MD5) hash value for each of them. Then combines hashes, takes the first 8 bytes of the hash of the resulting string, and interprets them as `UInt64` in big-endian byte order.
 
 ``` sql
 halfMD5(par1, ...)
@@ -54,7 +54,7 @@ sipHash64(par1,...)
 
 This is a cryptographic hash function. It works at least three times faster than the [MD5](#hash_functions-md5) function.
 
-Function [interprets](../../sql-reference/functions/type-conversion-functions.md#type_conversion_function-reinterpretAsString) all the input parameters as strings and calculates the hash value for each of them. Then combines hashes by the following algorithm:
+Function [interprets](../../sql-reference/functions/type-conversion-functions.md#type_conversion_functions-reinterpretAsString) all the input parameters as strings and calculates the hash value for each of them. Then combines hashes by the following algorithm:
 
 1.  After hashing all the input parameters, the function gets the array of hashes.
 2.  Function takes the first and the second elements and calculates a hash for the array of them.