1. 07 Oct, 2010 1 commit
    • Martin Hansson's avatar
      Bug#56423: Different count with SELECT and CREATE SELECT queries · 9c82ecec
      Martin Hansson authored
      This is a regression from the fix for bug no 38999. A storage engine capable
      of reading only a subset of a table's columns updates corresponding bits in
      the read buffer to signal that it has read NULL values for the corresponding
      columns. It cannot, and should not, update any other bits. Bug no 38999
      occurred because the implementation of UPDATE statements compare the NULL bits
      using memcmp, inadvertently comparing bits that were never requested from the
      storage engine. The regression was caused by the storage engine trying to
      alleviate the situation by writing to all NULL bits, even those that it had no
      knowledge of. This has devastating effects for the index merge algorithm,
      which relies on all NULL bits, except those explicitly requested, being left
      unchanged.
      
      The fix reverts the fix for bug no 38999 in both InnoDB and InnoDB plugin and
      changes the server's method of comparing records. For engines that always read
      entire rows, we proceed as usual. For engines capable of reading only select
      columns, the record buffers are now compared on a column by column basis. An
      assertion was also added so that non comparable buffers are never read. Some
      relevant copy-pasted code was also consolidated in a new function.
      9c82ecec
  2. 05 Oct, 2010 8 commits
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