db-derby-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-2991) Index split deadlock
Date Thu, 18 Dec 2008 18:17:44 GMT

     [ https://issues.apache.org/jira/browse/DERBY-2991?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Knut Anders Hatlen updated DERBY-2991:
--------------------------------------

    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.

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.


Mime
View raw message