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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DERBY-5153) Intermittent ASSERT FAILED Internal Error-- statistics not found in selectivityForConglomerate when running InterruptResilienceTest
Date Fri, 01 Apr 2011 12:10:05 GMT

     [ https://issues.apache.org/jira/browse/DERBY-5153?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Knut Anders Hatlen updated DERBY-5153:

    Attachment: remove-asserts.diff

I'm attaching a patch that removes the asserts and enables the test case.

Before the patch, if the statistics couldn't be found by non-debug builds, different heuristics
for the selectivity would be used depending on where it detected that statistics were missing.

If it was detected near the start of selectivityForConglomerate(), it would estimate the selectivity
to 0.1^(numKeys+1). But if it was detected later in the method, 0.1 would be returned.

I think the first estimate is the best one, as it sounds reasonable that the selectivity is
reduced (fewer rows match) the more columns we specify in the predicates. However, I believe
it was a typo in the original code that made it estimate the selectivity as 0.1^(numKeys+1)
and not as 0.1^numKeys. I've therefore removed both of the original heuristics and replaced
them with one single heuristic which is 0.1^numKeys.

The reason why I think the original calculation has a typo, is that other places in the code
we usually calculate selectivity in a way similar to this:

double selectivity = 1.0;
for (int i = 0; i < predicates; i++) {
    selectivity *= <selectivity for predicate i>;

In selectivityForConglomerate, the selectivity is initialized to 0.1 instead of 1.0, apparently
for no good reason. Apart from not being consistent with other calculations, it has some strange
effects on the boundaries, like the selectivity for numKeys=0, that is the selectivity for
TRUE, becomes 0.1, whereas it clearly should be 1.0.

In any case, the accuracy of the heuristic is probably not very important in this case. This
will only happen if the compilation of a query happens to come to this code in the short window
between dropping of the old statistics and inserting the new statistics. And recreation of
statistics invalidates the query plan, so the query is likely to be recompiled with fresh
statistics very soon afterwards.

> Intermittent ASSERT FAILED Internal Error-- statistics not found in selectivityForConglomerate
when running InterruptResilienceTest
> -----------------------------------------------------------------------------------------------------------------------------------
>                 Key: DERBY-5153
>                 URL: https://issues.apache.org/jira/browse/DERBY-5153
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions:
>            Reporter: Dag H. Wanvik
>            Assignee: Knut Anders Hatlen
>         Attachments: D5153.java, derby.log, remove-asserts.diff, test.diff
> Cf the enclosed derby.log:
> While executing this statement: "select * from mtTab where i=?", we see this stacktrace:
> org.apache.derby.shared.common.sanity.AssertFailure: ASSERT FAILED Internal Error-- statistics
not found in selectivityForConglomerate.
>  cd = ConglomerateDescriptor: conglomerateNumber = 1249 name = SQL110325154339720 uuid
= f04340b7-012e-ed78-50c3-00005e21fe7a indexable = true
> numKeys = 1
> 	at org.apache.derby.shared.common.sanity.SanityManager.THROWASSERT(SanityManager.java:162)
> 	at org.apache.derby.shared.common.sanity.SanityManager.THROWASSERT(SanityManager.java:147)
> 	at org.apache.derby.iapi.sql.dictionary.TableDescriptor.selectivityForConglomerate(TableDescriptor.java:1443)
> 	at org.apache.derby.impl.sql.compile.PredicateList.selectivity(PredicateList.java:3903)
> 	at org.apache.derby.impl.sql.compile.FromBaseTable.estimateCost(FromBaseTable.java:1295)
> 	at org.apache.derby.impl.sql.compile.OptimizerImpl.estimateTotalCost(OptimizerImpl.java:2626)
> 	at org.apache.derby.impl.sql.compile.OptimizerImpl.costBasedCostOptimizable(OptimizerImpl.java:2172)
> 	at org.apache.derby.impl.sql.compile.OptimizerImpl.costOptimizable(OptimizerImpl.java:1985)
> 	at org.apache.derby.impl.sql.compile.FromBaseTable.optimizeIt(FromBaseTable.java:526)
> 	at org.apache.derby.impl.sql.compile.ProjectRestrictNode.optimizeIt(ProjectRestrictNode.java:316)
> 	at org.apache.derby.impl.sql.compile.OptimizerImpl.costPermutation(OptimizerImpl.java:1939)
> 	at org.apache.derby.impl.sql.compile.SelectNode.optimize(SelectNode.java:1916)
> 	at org.apache.derby.impl.sql.compile.DMLStatementNode.optimizeStatement(DMLStatementNode.java:315)
> 	at org.apache.derby.impl.sql.compile.CursorNode.optimizeStatement(CursorNode.java:587)
> 	at org.apache.derby.impl.sql.GenericStatement.prepMinion(GenericStatement.java:384)
> 	at org.apache.derby.impl.sql.GenericStatement.prepare(GenericStatement.java:85)
> 	at org.apache.derby.impl.sql.GenericPreparedStatement.rePrepare(GenericPreparedStatement.java:229)
> 	at org.apache.derby.impl.sql.GenericPreparedStatement.executeStmt(GenericPreparedStatement.java:409)
> 	at org.apache.derby.impl.sql.GenericPreparedStatement.execute(GenericPreparedStatement.java:317)
> 	at org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(EmbedStatement.java:1242)
> 	at org.apache.derby.impl.jdbc.EmbedPreparedStatement.executeStatement(EmbedPreparedStatement.java:1686)
> 	at org.apache.derby.impl.jdbc.EmbedPreparedStatement.executeQuery(EmbedPreparedStatement.java:284)
> 	at org.apache.derbyTesting.functionTests.tests.store.InterruptResilienceTest$WorkerThread.run(InterruptResilienceTest.java:414)
> I saw this twice with the enclosed patch to InterruptResilienceTest (adds a test case
in preparation for DERBY-5152) - but the error occurs before we execute that fixture, so I
think the patch is irrelevant (a third and fourth execution failed to show the issue). I am
posting it here in case somebody can guess what could be wrong, I'll run more experiments
to see if I can reproduce it. Could it be related to our new index statistics daemon?

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