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  1. Derby
  2. DERBY-5258

btree post commit releases latch before committing/aborting purges, possibly allowing other operation on page



    • Bug
    • Status: Closed
    • Major
    • Resolution: Fixed
    • Store
    • None
    • High Value Fix
    • Crash, Data corruption


      From code inspection found the following problem. BTreePostCommit.purgeCommittedDeletes gives up the latch in it's finally block, before the internal transaction is
      committed. The transaction is committed no sync upon return from this routine leaving a very small window when some other thread could get latch on the page and
      perform operations on the page.

      This can be a problem if for some reason the internal transaction is never committed. Purges actually return space to the page, unlike deletes. In order to backout the
      purges one must add the rows back, taking up space on the page. If another tranaction comes in before the internal transaction is committed and does inserts there may
      be no space for the backout of the purges. This is why normal delete processing only sets flags on the rows and purge processing is handled differently.

      I found this problem while debugging a database submitted as part of DERBY-5248. I believe this issue can cause the problem there, but since we have no repro have
      decided to create a new issue to target this specific problem/solution. Later can close the other issue if it can never be reproduce after the fix. In DEBY-5248 there
      are purges without a commit followed immediated by an insert in another transaction that is commited and the purge transaction is never committed. On recovery the
      system tries to abort the internal transaction and eventually trashes the page when it does not actually have enough space to abort the purge. See that issue for more


        1. DERBY-5258_diff.txt
          11 kB
          Mike Matrigali

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