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Add additional heuristics to the algorithm for locating an optimal split location. New logic identifies localized monotonically increasing values in indexes with multiple columns. When this insertion pattern is detected, page splits split just after the new item that provoked a page split (or apply leaf fillfactor in the style of a rightmost page split). This optimization is a variation of the long established leaf fillfactor optimization used during rightmost page splits. 50/50 page splits are only appropriate with a pattern of truly random insertions, where the average space utilization ends up at 65% - 70%. Without this patch, affected cases have leaf pages that are no more than about 50% full on average. Future insertions can never make use of the free space left behind. With this patch, affected cases have leaf pages that are about 90% full on average (assuming a fillfactor of 90). Localized monotonically increasing insertion patterns are presumed to be fairly common in real-world applications. There is a fair amount of anecdotal evidence for this. Both pg_depend system catalog indexes (pg_depend_depender_index and pg_depend_reference_index) are at least 20% smaller after the regression tests are run when the optimization is available. Furthermore, many of the indexes created by a fair use implementation of TPC-C for Postgres are consistently about 40% smaller when the optimization is available. Note that even pg_upgrade'd v3 indexes make use of this optimization. Author: Peter Geoghegan Reviewed-By: Heikki Linnakangas Discussion: https://postgr.es/m/CAH2-WzkpKeZJrXvR_p7VSY1b-s85E3gHyTbZQzR0BkJ5LrWF_A@mail.gmail.com |
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