[jira] [Created] (JENA-570) Improve Fuseki/TDB transaction memory usage

["Stephen Allen (JIRA)" <ji...@apache.org>]

Stephen Allen created JENA-570:
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             Summary: Improve Fuseki/TDB transaction memory usage
                 Key: JENA-570
                 URL: https://issues.apache.org/jira/browse/JENA-570
             Project: Apache Jena
          Issue Type: Improvement
          Components: TDB
            Reporter: Stephen Allen
            Assignee: Stephen Allen


TDB has to buffer in memory all of the modified blocks for a transaction before committing it.  This causes out of memory exceptions when attempting to add a large number of statements in a single transaction.

An easy way to fix this would be to copy the write block contents into a memory mapped file instead of heap memory ^†^.  We can provide three user specified options for controlling the location of the temporary blocks:
# JVM heap (default, and what we currently use)
# Direct memory (process heap, but not in the JVM)
# Memory mapped temporary file

See this [Jena thread| http://markmail.org/thread/ckeevvhl2luevixw] for some additional discussion.

^†^ _The harder way would involve writing the old blocks to the journal, then writing the new blocks directly to the indexes, with a tombstone pointing to the old block in the journal so that readers could still retrieve the old version.  This however would seem to require a substantial refactor, as well as a change to the on-disk database format._



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