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From "Ramin Baradari (JIRA)" <j...@apache.org>
Subject [jira] [Created] (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 Fri, 16 Sep 2011 13:06:08 GMT
SYSCS_COMPRESS_TABLE causes an OutOfMemoryError when the heap is full at call time and then
gets mostly garbage collected later on
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                 Key: DERBY-5416
                 URL: https://issues.apache.org/jira/browse/DERBY-5416
             Project: Derby
          Issue Type: Bug
          Components: Store
    Affects Versions: 10.8.1.2, 10.7.1.1, 10.6.2.1
            Reporter: Ramin Baradari
            Priority: Critical


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.

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