[
https://issues.apache.org/jira/browse/DERBY-2991?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Knut Anders Hatlen updated DERBY-2991:
--------------------------------------
Derby Info: [Patch Available]
I know there are at least a couple of issues with the 2a patch, but
I'm setting the patch available flag anyway because I believe those
issues won't cause big changes to the patch, so the patch is in such a
state that it should be ready for review.
The issues I'm aware of that need to be resolved, are these:
- BTreePostCommit.purgeCommittedDeletes() needs to call
Page.setRepositionNeeded() to tell index scans that they need to
reposition by key. Since purgeCommittedDeletes() is only called in a
separate transaction that has an exclusive table lock, I believe
that this issue could only affect holdable index scans that
reposition after a commit.
- Some callers of BTreeScan.reposition(pos,false) have
comments/asserts stating that it is impossible that the current row
has been purged because they hold the scan lock. I think that it is
now possible that rows are purged from the page if we released the
latch, so we might need to change how they handle that situation. In
most cases (except read-uncommitted scans) the scans hold a lock on
the current row so that it is true that the row cannot have been
purged.
Feedback on the patch as it is would be appreciated. I'll probably be
offline for a couple of days, so I may not respond immediately to
questions/comments.
> 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: d2991-2a.diff, d2991-2a.stat, 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, d2991-preview-1e.diff, derby.log,
> InsertSelectDeadlock.java, perftest.diff, Repro2991.java,
> stacktraces_during_deadlock.txt, test-1.diff, test-2.diff, test-3.diff
>
>
> 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.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
