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-5416) SYSCS_COMPRESS_TABLE causes an OutOfMemoryError when the heap is full at call time and then gets mostly garbage collected later on
Date Tue, 10 Dec 2013 15:57:07 GMT

     [ https://issues.apache.org/jira/browse/DERBY-5416?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Knut Anders Hatlen updated DERBY-5416:
--------------------------------------

    Attachment: d5416-1a.diff

The attached patch, d5416-1a.diff, implements the variant of 1) mentioned above, where we
simply replace the initial memory usage with the current memory usage if we detect that the
memory usage has gone down.

Although this is not a perfect solution (the memory estimates are still inaccurate), I don't
think it will make the estimates worse in any situations. In the common case, it won't affect
the estimates at all. And when it does affect the estimates, it changes them from "way too
low" (negative values) to just "too low".

All the regression tests ran cleanly with the patch. So did Ramin's test case.

> SYSCS_COMPRESS_TABLE causes an OutOfMemoryError when the heap is full at call time and
then gets mostly garbage collected later on
> ----------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: DERBY-5416
>                 URL: https://issues.apache.org/jira/browse/DERBY-5416
>             Project: Derby
>          Issue Type: Bug
>          Components: Store
>    Affects Versions: 10.6.2.1, 10.7.1.1, 10.8.1.2
>            Reporter: Ramin Baradari
>            Assignee: Knut Anders Hatlen
>            Priority: Critical
>              Labels: derby_triage10_9
>         Attachments: compress_test_5416.patch, d5416-1a.diff, lowmem-test.diff
>
>
> When compressing a table with an index that is larger than the maximum heap size and
therefore cannot be hold in memory as a whole an OutOfMemoryError can occur. 
> For this to happen the heap usage must be close to the maximum heap size at the start
of the index recreation and then while the entries are sorted a garbage collection run must
clean out most of the heap. This can happen because a concurrent process releases a huge chunk
of memory or just because the buffer of a previous table compression has not yet been garbage
collected. 
> The internally used heuristics to guess when more memory can be used for the merge inserter
estimates that more memory is available and then the sort buffer gets doubled. The buffer
size gets doubled until the heap usage is back to the level when the merge inserter was first
initialized or when the OOM occurs.
> The problem lies in MergeInsert.insert(...). The check if the buffer can be doubled contains
the expression "estimatedMemoryUsed < 0" where estimatedMemoryUsed is the difference in
current heap usage and heap usage at initialization. Unfortunately, in the aforementioned
scenario this will be true until the heap usage will reach close to maximum heap size before
doubling the buffer size will be stopped.
> I've tested it with 10.6.2.1, 10.7.1.1 and 10.8.1.2 but the actual bug most likely exists
in prior versions too.



--
This message was sent by Atlassian JIRA
(v6.1.4#6159)

Mime
View raw message