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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3099) Possible bug in interaction with buffer manager causing pages not to be freed on rollback to savepoint
Date Wed, 10 Oct 2007 15:20:51 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3099?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12533766
] 

Bryan Pendleton commented on DERBY-3099:
----------------------------------------

Patch d3099-1.diff seems like a good patch to me. My only suggestion is
that I think you could place a comment into the code around line 700,
noting that the order of operations here is important, something along
the lines of:

  // Note that the slotFieldSize and slotEntrySize need to be
  // calculated BEFORE initSpace() is called, because the
  // maxFieldSize computation in initSpace() includes these
  // values in its calculations.

The comment at line 3355 is good, too, but it is somewhat 
discontiguous from the order-critical portion of your change.

Whether or not you think an extra comment would help, +1 to commit from me.


> 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
>            Assignee: Knut Anders Hatlen
>         Attachments: assert.diff, d3099-1.diff, failfast.diff, initSpace.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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