" In a nutshell, filesort() does quicksort on chunks of data that fit into its memory and then uses mergesort approach to merge the chunks. / if the sorted data doesn’t fit into memory (i.e. there is more than one chunk), filesort uses a temporary file to store the chunks. "
In last couple of weeks there has been a tide of ORDER/GROUP BY-related optimization bugs, where I was the fixer or the reviewer. This wasn’t an easy job because there is no sane description of how...
" In a nutshell, filesort() does quicksort on chunks of data that fit into its memory and then uses mergesort approach to merge the chunks. / if the sorted data doesn’t fit into memory (i.e. there is more than one chunk), filesort uses a temporary file to store the chunks. "
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How MySQL executes ORDER BY
In last couple of weeks there has been a tide of ORDER/GROUP BY-related optimization bugs, where I was the fixer or the reviewer. This wasn’t an easy job because there is no sane description of how...
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