[GitHub] [hadoop] slfan1989 commented on a diff in pull request #5673: YARN-8337. [FederationStateStore - MySql] Improve ApplicationHome Mysql Script.

["slfan1989 (via GitHub)" <gi...@apache.org>]

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">
   
   
   



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