From c3dd968931e31db7bc59483b85e67acc961dbafd Mon Sep 17 00:00:00 2001
From: bharatnc <bharatnc@gmail.com>
Date: Mon, 31 Aug 2020 21:42:27 -0700
Subject: [PATCH] fix ALTER LIVE VIEW lock issue

This PR fixes a lock issue that happens while executing
`ALTER LIVE VIEW` query with the `REFRESH` command that
results in a exception. The problem is that lock is currently
being acquired in `InterpreterALterQuery.cpp`
in the `InterpreterAlterQuery::execute()` method and lock
is again being reacquired in `StorageLiveView.cpp` in the
` StorageLiveView::refresh` method. This removes that extra
lock.

Before fix:

```sql
--create table

CREATE TABLE test0 (
    c0 UInt64
) ENGINE = MergeTree() PARTITION BY c0 ORDER BY c0;

-- enable experimental_live_view

:) SET allow_experimental_live_view=1

-- create live view;

:) CREATE LIVE VIEW live1 AS SELECT * FROM table0;

-- alter live view results in exception

:) ALTER LIVE VIEW live1 REFRESH;

...
...

Received exception from server (version 20.8.1):
Code: 49. DB::Exception: Received from localhost:9000. DB::Exception: RWLockImpl::getLock(): RWLock is already locked in exclusive mode.

```

After fix:

```sql
:)  ALTER LIVE VIEW live1 REFRESH;

ALTER LIVE VIEW live1
    REFRESH

Ok.

0 rows in set. Elapsed: 0.016 sec.
```
---
 src/Interpreters/InterpreterAlterQuery.cpp | 2 +-
 src/Storages/LiveView/StorageLiveView.cpp  | 5 +++--
 src/Storages/LiveView/StorageLiveView.h    | 2 +-
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/Interpreters/InterpreterAlterQuery.cpp b/src/Interpreters/InterpreterAlterQuery.cpp
index e0313803e9a..8cf581eb463 100644
--- a/src/Interpreters/InterpreterAlterQuery.cpp
+++ b/src/Interpreters/InterpreterAlterQuery.cpp
@@ -101,7 +101,7 @@ BlockIO InterpreterAlterQuery::execute()
             switch (command.type)
             {
                 case LiveViewCommand::REFRESH:
-                    live_view->refresh(context);
+                    live_view->refresh();
                     break;
             }
         }
diff --git a/src/Storages/LiveView/StorageLiveView.cpp b/src/Storages/LiveView/StorageLiveView.cpp
index 54ac5bcc791..4da02365232 100644
--- a/src/Storages/LiveView/StorageLiveView.cpp
+++ b/src/Storages/LiveView/StorageLiveView.cpp
@@ -518,9 +518,10 @@ void StorageLiveView::drop()
     condition.notify_all();
 }
 
-void StorageLiveView::refresh(const Context & context)
+void StorageLiveView::refresh()
 {
-    auto table_lock = lockExclusively(context.getCurrentQueryId(), context.getSettingsRef().lock_acquire_timeout);
+    // Lock is already acquired exclusively from InterperterAlterQuery.cpp InterpreterAlterQuery::execute() method.
+    // So, reacquiring lock is not needed and will result in an exception.
     {
         std::lock_guard lock(mutex);
         if (getNewBlocks())
diff --git a/src/Storages/LiveView/StorageLiveView.h b/src/Storages/LiveView/StorageLiveView.h
index 43afd169a92..0c099d01a29 100644
--- a/src/Storages/LiveView/StorageLiveView.h
+++ b/src/Storages/LiveView/StorageLiveView.h
@@ -122,7 +122,7 @@ public:
     void startup() override;
     void shutdown() override;
 
-    void refresh(const Context & context);
+    void refresh();
 
     Pipe read(
         const Names & column_names,