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order byとsortに関するyassのブックマーク (1)

  • What exactly is read_rnd_buffer_size

    Looking for documentation for read_rnd_buffer_size you would find descriptions such as “The read_rnd_buffer_size is used after a sort, when reading rows in sorted order. If you use many queries with ORDER BY, upping this can improve performance” which is cool but it does not really tell you how exactly read_rnd_buffer_size works as well as which layer it corresponds to – SQL or storage engine. Hon

    yass
    yass 2013/10/20
    " MySQL takes bunch of pointers from sort_buffer (just enough so all rows fit in read_rnd_buffer as they are read) and sorts them by row pointer, when performs reading into read_rnd_buffer in the sorted order – it can be pretty much sequential if you’re lucky. "
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