Details
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Bug
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Status: Closed (View Workflow)
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Major
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Resolution: Duplicate
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2.1.6
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None
Description
When a ReadWriteSplit session executes a read-only query outside of a transaction, it will get routed to a slave. When this happens, MaxScale does not use the master connection at all. Therefore, if a session executes only read-only queries, then its master connection could be allowed to time out due to wait_timeout.
This can easily be reproduced with the following:
mysql -h 127.0.0.1 -u maxscale -ppassword <<EOF
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CREATE DATABASE IF NOT EXISTS db1;
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CREATE TABLE IF NOT EXISTS db1.tab (str varchar(50));
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SET wait_timeout=10;
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SELECT 1;
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SELECT SLEEP(5);
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SELECT 1;
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SELECT SLEEP(5);
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SELECT 1;
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SELECT SLEEP(5);
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INSERT INTO db1.tab (str) VALUES ('str');
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EOF
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Output:
[ec2-user@ip-172-30-0-106 ~]$ mysql -h 127.0.0.1 -u maxscale -ppassword <<EOF
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> CREATE DATABASE IF NOT EXISTS db1;
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> CREATE TABLE IF NOT EXISTS db1.tab (str varchar(50));
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> SET wait_timeout=10;
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> SELECT 1;
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> SELECT SLEEP(5);
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> SELECT 1;
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> SELECT SLEEP(5);
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> SELECT 1;
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> SELECT SLEEP(5);
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> INSERT INTO db1.tab (str) VALUES ('str');
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> EOF
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1
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1
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SLEEP(5)
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0
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1
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1
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SLEEP(5)
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0
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1
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1
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ERROR 2013 (HY000) at line 9: Lost connection to MySQL server during query
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If this problem is encounted in a Java application, then the error is a bit different. I've also attached a Java program that can be used to reproduce the issue.
Output:
[ec2-user@ip-172-30-0-106 ~]$ export CLASSPATH='/home/ec2-user/mariadb-java-client-2.1.0.jar:.'
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[ec2-user@ip-172-30-0-106 ~]$ javac ./TestMasterConnIdle.java
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[ec2-user@ip-172-30-0-106 ~]$ java TestMasterConnIdle
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Checking thread 10.
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Checking thread 8.
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Checking thread 11.
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Checking thread 9.
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Checking thread 10.
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Checking thread 8.
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Checking thread 11.
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SQLException: (conn:2073) Could not send query: unexpected end of stream, read 0 bytes from 4
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SQLState: 08
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VendorError: 0
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Checking thread 9.
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Checking thread 10.
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SQLException: (conn:2074) Could not send query: unexpected end of stream, read 0 bytes from 4
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SQLState: 08
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VendorError: 0
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Checking thread 8.
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SQLException: (conn:2072) Could not send query: unexpected end of stream, read 0 bytes from 4
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SQLState: 08
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VendorError: 0
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Checking thread 9.
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SQLException: (conn:2075) Could not send query: unexpected end of stream, read 0 bytes from 4
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SQLState: 08
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VendorError: 0
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As a potential fix, maybe ReadWriteSplit should route a COM_PING to a session's master connection whenever a query is routed to a slave connection?
