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https://issues.apache.org/jira/browse/DERBY-2991?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Knut Anders Hatlen updated DERBY-2991:
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Attachment: perftest.diff
Here's a small performance test that I wrote. It extends the JDBCPerfTestCase
class in the JUnit framework. All the tests use a table with 1000 rows. The
table has 13 columns: one VARCHAR(10), one VARCHAR(100), one VARCHAR(1000) and
ten DECIMAL(10,10). Each single VARCHAR column has an index, one compound index
is covering all the VARCHAR columns, there's an index on one of the DECIMAL
columns, and there's one covering all the DECIMAL columns. For each index,
there's a test case that simply runs through the entire index.
After a couple of repeated runs I can't say that saving the position looks more
expensive than locking the scan. Actually, the tests appear to perform slightly
better when the position is saved, at least that's what it looks like in my
environment (OpenSolaris 2008.11, Java 1.6.0_10). (Except that in some cases it
fails because the JUnit framework compresses all the tables before starting the
test, and the problem with pages changing from leaf to branch mentioned in my
previous comment surfaces.) I'll need to run the tests more in order to say
anything for sure. I will do that and report back.
Does anyone have suggestions for any other performance tests we should run to
check if this is an appropriate path to follow?
> 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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