SYSCS_UPDATE_STATISTICS takes unnecessary table lock
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Key: DERBY-4274
URL: https://issues.apache.org/jira/browse/DERBY-4274
Project: Derby
Issue Type: Bug
Components: SQL
Affects Versions: 10.5.1.1
Reporter: Knut Anders Hatlen
Assignee: Knut Anders Hatlen
I'm using SYSCS_UTIL.SYSCS_UPDATE_STATISTICS in an application and see
deadlocks similar to this one from time to time:
Caused by: java.sql.SQLTransactionRollbackException: A lock could not be
obtained due to a deadlock, cycle of locks and waiters is:
Lock : ROW, SYSSTATISTICS, (2,20)
Waiting XID : {20137, S} , APP, SELECT CS.REVISION, A.NAME, CS.TIME,
CS.MESSAGE, F2.PATH FROM CHANGESETS CS, FILECHANGES FC, REPOSITORIES R, FILES
F, AUTHORS A, FILECHANGES FC2, FILES F2 WHERE R.PATH = ? AND F.PATH LIKE ?
ESCAPE '#' AND F.REPOSITORY = R.ID AND A.REPOSITORY = R.ID AND CS.ID =
FC.CHANGESET AND R.ID = CS.REPOSITORY AND FC.FILE = F.ID AND A.ID = CS.AUTHOR
AND CS.ID = FC2.CHANGESET AND FC2.FILE = F2.ID ORDER BY CS.ID DESC
Granted XID : {20134, X}
Lock : TABLE, CHANGESETS, Tablelock
Waiting XID : {20134, X} , APP, alter table "APP"."CHANGESETS" all update
statistics
Granted XID : {20137, IS}
. The selected victim is XID : 20137.
Here, a select statement is being re-prepared because update statistics has
invalidated it, but it has to wait for update statistics to finish in order to
read the new statistics from SYSSTATISTICS. Then update statistics attempts to
obtain an exclusive lock on the table whose indexes are being updated, but it
has to wait because the select statement is holding an intention lock on the
table. Both transactions wait for each other, so we have a deadlock.
Since SYSCS_UPDATE_STATISTICS does not update the table, only its entries in
SYSSTATISTICS, there is no need to take an exclusive table lock. If it didn't
lock the table exclusively, this deadlock situation would go away.
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