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https://issues.apache.org/jira/browse/DERBY-3099?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12533135
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Knut Anders Hatlen commented on DERBY-3099:
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OK, so I found out why firstFreeByte/freeSpace/totalSpace were different (see
DERBY-3116), but that doesn't seem to be the problem. I'll keep looking.
> Possible bug in interaction with buffer manager causing pages not to be freed
> on rollback to savepoint
> ------------------------------------------------------------------------------------------------------
>
> Key: DERBY-3099
> URL: https://issues.apache.org/jira/browse/DERBY-3099
> Project: Derby
> Issue Type: Bug
> Components: Services, Store
> Affects Versions: 10.4.0.0
> Reporter: Knut Anders Hatlen
> Attachments: failfast.diff
>
>
> I noticed this strange behaviour when I was working on DERBY-2911. It seems
> like the result of test case P042 in unit/T_RawStoreFactory.unit is dependent
> on the actual contents of the buffer manager (which pages have been evicted,
> which free entries have been reused and so on). I'm not sure if this is a bug
> in the test or somewhere in the code, or if this is expected behaviour, but
> it sounds a bit suspicious.
> For instance, commenting out all the test cases preceeding P042 makes P042
> fail, even though P042 creates a new container so that it should not be
> affected by any of the previous test cases. Also, commenting out a space
> optimization in Clock.findFreeItem() so that freed entries are not reused
> except when rotateClock() is called on a full cache to find a victim, causes
> the test case to fail. A third way to make it fail, is to vary the scan
> direction when looking for a free entry to reuse in the new buffer manager
> (ConcurrentCache). If the scan is disabled or walks the clock from the
> beginning to the end, the test fails, but if the clock is scanned backwards,
> it passes.
> The code that fails in the test, is
> c = t_util.t_openContainer(t, segment, cid, true);
> Page checkNextPage = t_util.t_addPage(c);
> if (checkNextPage.getPageNumber() == nextPageNumber)
> throw T_Fail.testFailMsg(
> "expect some pages to be freed by
> update rollback");
> The expected page number is 2, and the actual page number is 7.
> Before this, a large row has been inserted on page 1 and overflows to page 2,
> 3, 4, 5 and 6. Also, page 7 has been added manually before all the updates
> were rolled back so that the pages from 2 up to 7 should be unallocated. Page
> 7 is then added and removed, and the transaction is committed. After
> reopening the container, the test expects the pages from 2 up to 7 to be
> free, and that t_addPage() should allocate page number 2.
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