slfan1989 commented on code in PR #5673:
URL: https://github.com/apache/hadoop/pull/5673#discussion_r1209399807
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hadoop-yarn-project/hadoop-yarn/bin/FederationStateStore/MySQL/FederationStateStoreStoredProcs.sql:
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@@ -92,12 +92,9 @@ CREATE PROCEDURE sp_addApplicationHomeSubCluster(
IN applicationContext_IN BLOB,
OUT storedHomeSubCluster_OUT varchar(256), OUT rowCount_OUT int)
BEGIN
- INSERT INTO applicationsHomeSubCluster
- (applicationId, homeSubCluster, createTime, applicationContext)
- (SELECT applicationId_IN, homeSubCluster_IN, NOW(), applicationContext_IN
- FROM applicationsHomeSubCluster
- WHERE applicationId = applicationId_IN
- HAVING COUNT(*) = 0 );
+ INSERT IGNORE INTO applicationsHomeSubCluster(
Review Comment:
Thank you very much for helping to review this pr!
`YARN-8337` describes a scenario where we use the Mysql database, and when
multiple sessions call the sp_addApplicationHomeSubCluster stored procedure at
the same time, a deadlock may occur.
MySQL Gap lock is a type of gap lock used to protect a range of gaps instead
of specific data rows. We can look at the following picture.
<img width="684" alt="image"
src="https://github.com/apache/hadoop/assets/55643692/bef31a2d-20b7-40b8-a007-0b3d07bffc65";>
When we need to write data to MySQL, for example
`application_1526528662010_001201`.
- Step1, we need to apply for a gap lock there is a gap lock between the
previous record(`application_1526528662010_001199`) and infinity. Prevent other
transactions from inserting new records in this range.
- Step2, After applying for the gap lock, `application_1526528662010_001201`
will apply for the row lock and complete the record writing.
If we have 3 different Sessions applying to insert different records at the
same time, SessionA writes `application_1526528662010_001201`, SessionB writes
`application_1526528662010_001202`, and SessionC writes
`application_1526528662010_001203`. They may hold different gap locks, but
need to acquire row locks at the same time to continue execution, resulting in
a deadlock.
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