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https://issues.apache.org/jira/browse/DERBY-4193?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mike Matrigali updated DERBY-4193:
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I believe your proposed change may result in a change in behavior for isolation
levels which don't
require previous key locking. In particular if you use previous key locking
code it may not get a lock
at all for some isolation levels. I am not sure how important it is, but the
difference I think is:
current code: It loops using the "fast" search until it can get a lock on the
last row in the last leaf page while holding latch and not waiting on lock.
change: in some isolation levels may not get lock in the position code, and
instead will fail to get lock
in fetchMax() code and give up earlier on the "fast" search in
case where there is competition
for the lock.
Reading through the comments in the code, I believe they are misleading. I
think they came from a
cut/paste of some prototype backward scan code and actually don't apply to the
specific max scan case.
> ASSERT FAILED Scan position already saved with multi-threaded
> insert/update/delete
> -----------------------------------------------------------------------------------
>
> Key: DERBY-4193
> URL: https://issues.apache.org/jira/browse/DERBY-4193
> Project: Derby
> Issue Type: Bug
> Components: Store
> Affects Versions: 10.5.1.1, 10.6.0.0
> Environment: Windows XP, IBM 1.6 SR6, Sun 1.6.0_01-b06
> Reporter: Kathey Marsden
> Assignee: Knut Anders Hatlen
> Attachments: d4193-1a.diff, ScanPosSaved.java, ScanPosSaved.java
>
>
> The attached program ScanPosSaved.java produces the error below, fairly
> quickly.
> The program has three threads, one doing inserts into a table with an
> identity column, one updating the row with the maximum id, one deleting the
> row with the maximum id.
> To reproduce, run >java ScanPosSaved and <ctrl> <c> out of the program after
> you get the error.
> I saw this 10.5 and trunk sane builds but did not see it on 10.4. With the
> insane build of 10.5.1.1 (RC2) I did not see any symptoms right away, so
> don't know how serious an issue this is for insane builds.
> org.apache.derby.shared.common.sanity.AssertFailure: ASSERT FAILED Scan
> position already saved
> at
> org.apache.derby.shared.common.sanity.SanityManager.ASSERT(SanityManager.java:120)
> at
> org.apache.derby.impl.store.access.btree.BTreeScan.savePositionAndReleasePage(BTreeScan.java:2148)
> at
> org.apache.derby.impl.store.access.btree.BTreeScan.savePositionAndReleasePage(BTreeScan.java:2212)
> at
> org.apache.derby.impl.store.access.btree.BTreeRowPosition.saveMeAndReleasePage(BTreeRowPosition.java:128)
> at
> org.apache.derby.impl.store.access.btree.index.B2IRowLocking3.lockRowOnPage(B2IRowLocking3.java:295)
> at
> org.apache.derby.impl.store.access.btree.index.B2IRowLocking3._lockScanRow(B2IRowLocking3.java:599)
> at
> org.apache.derby.impl.store.access.btree.index.B2IRowLockingRR.lockScanRow(B2IRowLockingRR.java:105)
> at
> org.apache.derby.impl.store.access.btree.BTreeMaxScan.positionAtStartPosition(BTreeMaxScan.java:347)
> at
> org.apache.derby.impl.store.access.btree.BTreeMaxScan.fetchMax(BTreeMaxScan.java:434)
> at
> org.apache.derby.impl.store.access.btree.index.B2I.fetchMaxOnBTree(B2I.java:739)
> at
> org.apache.derby.impl.store.access.RAMTransaction.fetchMaxOnBtree(RAMTransaction.java:1078)
> at
> org.apache.derby.impl.sql.execute.LastIndexKeyResultSet.openCore(LastIndexKeyResultSet.java:189)
> at
> org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.openCore(ProjectRestrictResultSet.java:168)
> at
> org.apache.derby.impl.sql.execute.ScalarAggregateResultSet.openCore(ScalarAggregateResultSet.java:133)
> at
> org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.openCore(ProjectRestrictResultSet.java:168)
> at
> org.apache.derby.impl.sql.execute.BasicNoPutResultSetImpl.open(BasicNoPutResultSetImpl.java:245)
> at
> org.apache.derby.impl.sql.GenericPreparedStatement.executeStmt(GenericPreparedStatement.java:416)
> at
> org.apache.derby.impl.sql.GenericPreparedStatement.execute(GenericPreparedStatement.java:297)
> at
> org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(EmbedStatement.java:1235)
> at
> org.apache.derby.impl.jdbc.EmbedStatement.execute(EmbedStatement.java:625)
> at
> org.apache.derby.impl.jdbc.EmbedStatement.executeQuery(EmbedStatement.java:152)
> at ScanPosSaved.updateOperation(ScanPosSaved.java:62)
> at ScanPosSaved$3.run(ScanPosSaved.java:17)
> I discovered this when trying to get a smaller repro for DERBY-4181, but I
> think it is a different issue, because it reproduces on multiple jvms and
> does not reproduce on 10.4. The assertion was added with DERBY-2991. Knut
> could you perhaps assess how serious this is?
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