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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DERBY-5752) LOBStreamControl should materialize less aggressively
Date Wed, 09 May 2012 13:17:52 GMT
Knut Anders Hatlen created DERBY-5752:

             Summary: LOBStreamControl should materialize less aggressively
                 Key: DERBY-5752
                 URL: https://issues.apache.org/jira/browse/DERBY-5752
             Project: Derby
          Issue Type: Improvement
          Components: JDBC
    Affects Versions:
            Reporter: Knut Anders Hatlen
            Assignee: Knut Anders Hatlen

The constructor LOBStreamControl(EmbedConnection, byte[]) always makes the buffer size equal
to the LOB size, effectively creating an extra, fully materialized copy of the LOB in memory.

I think the assumption here is that a LOB that's already materialized is a small one. That
is, LOBs that are smaller than 32 KB and fit in a single page are typically materialized when
read from store. However, we sometimes materialize LOBs that are a lot bigger than 32 KB.
For example, triggers that access LOBs may materialize them regardless of size (see comment
in DMLWriteResultSet's constructor for details). For these large LOBs, it sounds unreasonable
to allocate a buffer of the same size as the LOB itself.

I'd suggest that we change the constructor so that it never allocates a buffer larger than
32KB. That would mean that the behaviour is preserved for all LOBs fetched directly from store
(only LOBs that don't fit in a single page will cause temporary files to be created), whereas
we'll prevent large LOBs accessed by triggers from being duplicated in memory by overflowing
to temporary files.

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