From bb1ac2af8218b606a96f730eb7a1419b06a3c8ab Mon Sep 17 00:00:00 2001
From: taichong <tai_chong@foxmail.com>
Date: Thu, 29 Oct 2020 14:53:32 +0800
Subject: [PATCH] Shrink sequence gtid set

when use MySQL Master -> MySQL Slave -> ClickHouse MaterializeMySQL
Engine

and MySQL Slave enable slave_parallel_worker the gtid in .metadata won't
shrink.

Like this:

https://github.com/ClickHouse/ClickHouse/issues/15951
---
 src/Core/MySQL/MySQLGtid.cpp      | 12 ++++++++++++
 src/Core/MySQL/MySQLGtid.h        |  2 ++
 src/Core/tests/mysql_protocol.cpp | 11 +++++++++++
 3 files changed, 25 insertions(+)

diff --git a/src/Core/MySQL/MySQLGtid.cpp b/src/Core/MySQL/MySQLGtid.cpp
index df26eb7aa08..6e50998da62 100644
--- a/src/Core/MySQL/MySQLGtid.cpp
+++ b/src/Core/MySQL/MySQLGtid.cpp
@@ -85,6 +85,9 @@ void GTIDSets::update(const GTID & other)
                         ErrorCodes::LOGICAL_ERROR);
                 }
 
+                /// Try to shirnk Sequence interval.
+                GTIDSet::tryShirnk(set, i, current);
+
                 /// Sequence, extend the interval.
                 if (other.seq_no == current.end)
                 {
@@ -116,6 +119,15 @@ void GTIDSets::update(const GTID & other)
     sets.emplace_back(set);
 }
 
+void GTIDSet::tryShirnk(GTIDSet & set, unsigned int i, GTIDSet::Interval & current)
+{
+    if (i != set.intervals.size() -1) {
+        auto & next = set.intervals[i+1];
+        if (current.end == next.start)
+            set.tryMerge(i);
+    }
+}
+
 String GTIDSets::toString() const
 {
     WriteBufferFromOwnString buffer;
diff --git a/src/Core/MySQL/MySQLGtid.h b/src/Core/MySQL/MySQLGtid.h
index d228e269872..cd8cd0a2e98 100644
--- a/src/Core/MySQL/MySQLGtid.h
+++ b/src/Core/MySQL/MySQLGtid.h
@@ -26,6 +26,8 @@ public:
     std::vector<Interval> intervals;
 
     void tryMerge(size_t i);
+
+    static void tryShirnk(GTIDSet & set, unsigned int i, Interval & current) ;
 };
 
 class GTIDSets
diff --git a/src/Core/tests/mysql_protocol.cpp b/src/Core/tests/mysql_protocol.cpp
index 6cad095fc85..7e6aae5da23 100644
--- a/src/Core/tests/mysql_protocol.cpp
+++ b/src/Core/tests/mysql_protocol.cpp
@@ -260,6 +260,17 @@ int main(int argc, char ** argv)
              "10662d71-9d91-11ea-bbc2-0242ac110003:6-7",
              "20662d71-9d91-11ea-bbc2-0242ac110003:9",
              "10662d71-9d91-11ea-bbc2-0242ac110003:6-7,20662d71-9d91-11ea-bbc2-0242ac110003:9"},
+
+            {"shirnk-sequence",
+              "10662d71-9d91-11ea-bbc2-0242ac110003:1-3:4-5:7",
+             "10662d71-9d91-11ea-bbc2-0242ac110003:6",
+             "10662d71-9d91-11ea-bbc2-0242ac110003:1-7"},
+
+            {"shirnk-sequence",
+             "10662d71-9d91-11ea-bbc2-0242ac110003:1-3:4-5:10",
+             "10662d71-9d91-11ea-bbc2-0242ac110003:8",
+             "10662d71-9d91-11ea-bbc2-0242ac110003:1-5:8:10"
+            }
         };
 
         for (auto & tc : cases)