1. 09 Oct, 2006 2 commits
    • istruewing@chilla.local's avatar
      Merge chilla.local:/home/mydev/mysql-4.1-bug8283 · 1daa6a71
      istruewing@chilla.local authored
      into  chilla.local:/home/mydev/mysql-4.1-bug8283-one
      1daa6a71
    • istruewing@chilla.local's avatar
      Bug#8283 - OPTIMIZE TABLE causes data loss · 5f08a831
      istruewing@chilla.local authored
      OPTIMIZE TABLE with myisam_repair_threads > 1 performs a non-quick 
      parallel repair. This means that it does not only rebuild all 
      indexes, but also the data file.
      
      Non-quick parallel repair works so that there is one thread per 
      index. The first of the threads rebuilds also the new data file.
      
      The problem was that all threads shared the read io cache on the
      old data file. If there were holes (deleted records) in the table,
      the first thread skipped them, writing only contiguous, non-deleted
      records to the new data file. Then it built the new index so that
      its entries pointed to the correct record positions. But the other
      threads didn't know the new record positions, but put the positions
      from the old data file into the index.
      
      The new design is so that there is a shared io cache which is filled
      by the first thread (the data file writer) with the new contiguous
      records and read by the other threads. Now they know the new record
      positions.
      
      Another problem was that for the parallel repair of compressed
      tables a common bit_buff and rec_buff was used. I changed it so
      that thread specific buffers are used for parallel repair.
      
      A similar problem existed for checksum calculation. I made this
      multi-thread safe too.
      5f08a831
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