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Problem: ======= InnoDB persistent statistics doesn't take innodb_stats_method variable while calculating n_diff_pfx for the n-prefix index columns. Solution: ========= While calculating the persistent statistics, InnoDB consider all NULLS as different value when innodb_stats_method is set to NULLS_UNEQUAL or NULLS_IGNORED. InnoDB statistics depends on the value of "innodb_stats_method" variable when the statistics were last recalculated. dict_stats_analyze_index_level(), dict_stats_scan_page(), dict_stats_analyze_index_below_cur(), dict_stats_analyze_index_for_n_prefix(): All function accepts the parameter to indicate the innodb_stats_method. It also calculates the number of non-null key value for each level or leaf page dict_stats_index_set_n_diff(): calculates the number of non-null values similar to number of different key values. Append the non-default innodb_stats_method variable name for n_diff_pfx statistics description in mysql.innodb_index_stats. IndexScanStatistics: Structure to store the various statistical metric gathered during index scan fetch operation. This structure is being used in dict_stats_analyze_index_level() to fetch the statistics
25 lines
1 KiB
Text
25 lines
1 KiB
Text
--- innodb_stats_method.result
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+++ innodb_stats_method,NULLS_IGNORED.result
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@@ -7,16 +7,16 @@
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SELECT stat_name, stat_value, stat_description
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FROM mysql.innodb_index_stats WHERE database_name="test" and table_name="t1";
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stat_name stat_value stat_description
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-n_diff_pfx01 16341 DB_ROW_ID NULLS_UNEQUAL
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+n_diff_pfx01 16341 DB_ROW_ID NULLS_IGNORED
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n_leaf_pages 37 Number of leaf pages in the index
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size 97 Number of pages in the index
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-n_diff_pfx01 16384 f1 NULLS_UNEQUAL
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-n_diff_pfx02 16384 f1,f3 NULLS_UNEQUAL
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-n_diff_pfx03 16384 f1,f3,DB_ROW_ID NULLS_UNEQUAL
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+n_diff_pfx01 16384 f1 NULLS_IGNORED
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+n_diff_pfx02 16384 f1,f3 NULLS_IGNORED
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+n_diff_pfx03 16384 f1,f3,DB_ROW_ID NULLS_IGNORED
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n_leaf_pages 1 Number of leaf pages in the index
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size 19 Number of pages in the index
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-n_diff_pfx01 16384 f3 NULLS_UNEQUAL
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-n_diff_pfx02 16384 f3,DB_ROW_ID NULLS_UNEQUAL
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+n_diff_pfx01 16384 f3 NULLS_IGNORED
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+n_diff_pfx02 16384 f3,DB_ROW_ID NULLS_IGNORED
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n_leaf_pages 1 Number of leaf pages in the index
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size 15 Number of pages in the index
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SHOW KEYS FROM t1;
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