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https://issues.apache.org/jira/browse/DERBY-2991?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12658493#action_12658493
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Knut Anders Hatlen commented on DERBY-2991:
-------------------------------------------
I had the JUnit test running repeatedly over the weekend, 300 times
for each configuration to get a more reliable average. I've summarized
the results in the table below. Positive values in the increase column
means that trunk is faster, negative values means that the patched
version is faster.
TEST |TRUNK_TIME |PATCHED_TI&|INCREASE |INCREASE_PERCENT
-------------------------------------------------------------------------------
decimal10columns |17752 |17761 |9 |0.0506985128436277
decimal1column |4875 |4842 |-33 |-0.676923076923075
varchar10 |4586 |4517 |-69 |-1.5045791539467945
varchar100 |7288 |7185 |-103 |-1.4132821075740987
varchar1000 |35977 |37008 |1031 |2.865719765405683
varcharAll |41502 |42701 |1199 |2.8890173967519583
Not much difference between them. For smaller keys, it seems like
saving the position is slightly cheaper, whereas for larger keys it
appears to be slightly more expensive.
> Index split deadlock
> --------------------
>
> Key: DERBY-2991
> URL: https://issues.apache.org/jira/browse/DERBY-2991
> Project: Derby
> Issue Type: Bug
> Components: Store
> Affects Versions: 10.2.2.0, 10.3.1.4
> Environment: Windows XP, Java 6
> Reporter: Bogdan Calmac
> Assignee: Knut Anders Hatlen
> Attachments: d2991-preview-1a.diff, d2991-preview-1a.stat,
> d2991-preview-1b.diff, d2991-preview-1b.stat, d2991-preview-1c.diff,
> d2991-preview-1c.stat, d2991-preview-1d.diff, d2991-preview-1d.stat,
> derby.log, InsertSelectDeadlock.java, perftest.diff, Repro2991.java,
> stacktraces_during_deadlock.txt
>
>
> After doing dome research on the mailing list, it appears that the index
> split deadlock is a known behaviour, so I will start by describing the
> theoretical problem first and then follow with the details of my test case.
> If you have concurrent select and insert transactions on the same table, the
> observed locking behaviour is as follows:
> - the select transaction acquires an S lock on the root block of the index
> and then waits for an S lock on some uncommitted row of the insert transaction
> - the insert transaction acquires X locks on the inserted records and if it
> needs to do an index split creates a sub-transaction that tries to acquire an
> X lock on the root block of the index
> In summary: INDEX LOCK followed by ROW LOCK + ROW LOCK followed by INDEX LOCK
> = deadlock
> In the case of my project this is an important issue (lack of concurrency
> after being forced to use table level locking) and I would like to contribute
> to the project and fix this issue (if possible). I was wondering if someone
> that knows the code can give me a few pointers on the implications of this
> issue:
> - Is this a limitation of the top-down algorithm used?
> - Would fixing it require to use a bottom up algorithm for better
> concurrency (which is certainly non trivial)?
> - Trying to break the circular locking above, I would first question why
> does the select transaction need to acquire (and hold) a lock on the root
> block of the index. Would it be possible to ensure the consistency of the
> select without locking the index?
> -----
> The attached test (InsertSelectDeadlock.java) tries to simulate a typical
> data collection application, it consists of:
> - an insert thread that inserts records in batch
> - a select thread that 'processes' the records inserted by the other thread:
> 'select * from table where id > ?'
> The derby log provides detail about the deadlock trace and
> stacktraces_during_deadlock.txt shows that the inser thread is doing an index
> split.
> The test was run on 10.2.2.0 and 10.3.1.4 with identical behaviour.
> Thanks,
> Bogdan Calmac.
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