Jan Lindström 8bc5eabea8 MDEV-7084: innodb index stats inadequate using constant ... innodb_stats_sample_pages Analysis: If you set the number of analyzed pages to very low number compared to actual pages on that table/index it randomly pics those pages (default 8 pages), this leads to fact that query after analyze table returns different results. If the index tree is small, smaller than 10 * n_sample_pages + total_external_size, then the estimate is ok. For bigger index trees it is common that we do not see any borders between key values in the few pages we pick. But still there may be n_sample_pages different key values, or even more. And it just tries to approximate to n_sample_pages (8). Fix: (1) Introduced new dynamic configuration variable innodb_stats_sample_traditional that retains the current design. Default false. (2) If traditional sample is not used we use n_sample_pages = max(min(srv_stats_sample_pages, index->stat_index_size), log2(index->stat_index_size)* srv_stats_sample_pages); (3) Introduced new dynamic configuration variable stat_modified_counter (default = 0) if set sets lower bound for row updates when statistics is re-estimated. If user has provided upper bound for how many rows needs to be updated before we calculate new statistics we use minimum of provided value and 1/16 of table every 16th round. If no upper bound is provided (srv_stats_modified_counter = 0, default) then calculate new statistics if 1 / 16 of table has been modified since the last time a statistics batch was run. We calculate statistics at most every 16th round, since we may have a counter table which is very small and updated very often. @param t table @return true if the table has changed too much and stats need to be recalculated */ #define DICT_TABLE_CHANGED_TOO_MUCH(t) \ ((ib_int64_t) (t)->stat_modified_counter > (srv_stats_modified_counter ? \ ut_min(srv_stats_modified_counter, (16 + (t)->stat_n_rows / 16)) : \ 16 + (t)->stat_n_rows / 16))		2014-11-19 20:27:34 +02:00
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srv0srv.c	MDEV-7084: innodb index stats inadequate using constant	2014-11-19 20:27:34 +02:00
srv0start.c	merge with XtraDB 5.5.37-35.0	2014-06-03 09:53:10 +02:00