branches/5.1:

Fix Bug#43660 SHOW INDEXES/ANALYZE does NOT update cardinality for indexes
of InnoDB table

by replacing the PRNG that is used to pick random pages with a better
one.

This is based on r4670 but also adds a new configuration option and
enables the fix only if this option is changed. Please skip the present
revision when merging.

Approved by:	Heikki (via email)

handler/ha_innodb.cc

@@ -8261,6 +8261,14 @@ static MYSQL_SYSVAR_BOOL(stats_on_metadata, innobase_stats_on_metadata,
   "Enable statistics gathering for metadata commands such as SHOW TABLE STATUS (on by default)",
   NULL, NULL, TRUE);
 
+static MYSQL_SYSVAR_BOOL(use_legacy_cardinality_algorithm,
+  srv_use_legacy_cardinality_algorithm,
+  PLUGIN_VAR_OPCMDARG,
+  "Use legacy algorithm for picking random pages during index cardinality "
+  "estimation. Disable this to use a better algorithm, but note that your "
+  "query plans may change (enabled by default).",
+  NULL, NULL, TRUE);
+
 static MYSQL_SYSVAR_BOOL(adaptive_hash_index, innobase_adaptive_hash_index,
   PLUGIN_VAR_OPCMDARG | PLUGIN_VAR_READONLY,
   "Enable InnoDB adaptive hash index (enabled by default).  "
@@ -8396,6 +8404,7 @@ static struct st_mysql_sys_var* innobase_system_variables[]= {
   MYSQL_SYSVAR(open_files),
   MYSQL_SYSVAR(rollback_on_timeout),
   MYSQL_SYSVAR(stats_on_metadata),
+  MYSQL_SYSVAR(use_legacy_cardinality_algorithm),
   MYSQL_SYSVAR(adaptive_hash_index),
   MYSQL_SYSVAR(status_file),
   MYSQL_SYSVAR(support_xa),

include/srv0srv.h

@@ -235,6 +235,12 @@ extern ulint srv_read_ahead_seq;
 /* variable to count the number of random read-aheads were done */
 extern ulint srv_read_ahead_rnd;
 
+/* An option to enable the fix for "Bug#43660 SHOW INDEXES/ANALYZE does
+NOT update cardinality for indexes of InnoDB table". By default we are
+running with the fix disabled because MySQL 5.1 is frozen for such
+behavioral changes. */
+extern char srv_use_legacy_cardinality_algorithm;
+
 /* In this structure we store status variables to be passed to MySQL */
 typedef struct export_var_struct export_struc;
 

page/page0cur.c

@@ -15,6 +15,8 @@ Created 10/4/1994 Heikki Tuuri
 #include "mtr0log.h"
 #include "log0recv.h"
 #include "rem0cmp.h"
+#include "srv0srv.h"
+#include "ut0ut.h"
 
 static ulint	page_rnd	= 976722341;
 
@@ -23,6 +25,44 @@ static ulint	page_rnd	= 976722341;
 ulint	page_cur_short_succ	= 0;
 # endif /* UNIV_SEARCH_PERF_STAT */
 
+/***********************************************************************
+This is a linear congruential generator PRNG. Returns a pseudo random
+number between 0 and 2^64-1 inclusive. The formula and the constants
+being used are:
+X[n+1] = (a * X[n] + c) mod m
+where:
+X[0] = ut_usectime()
+a = 1103515245 (3^5 * 5 * 7 * 129749)
+c = 12345 (3 * 5 * 823)
+m = 18446744073709551616 (2^64)
+*/
+#define LCG_a	1103515245
+#define LCG_c	12345
+static
+unsigned long long
+page_cur_lcg_prng()
+/*===============*/
+			/* out: number between 0 and 2^64-1 */
+{
+	static unsigned long long lcg_current = 0;
+	static ibool		initialized = FALSE;
+	ulint			time_sec;
+	ulint			time_ms;
+
+	if (!initialized) {
+		ut_usectime(&time_sec, &time_ms);
+		lcg_current = (unsigned long long) (time_sec * 1000000
+						    + time_ms);
+		initialized = TRUE;
+	}
+
+	/* no need to "% 2^64" explicitly because lcg_current is
+	64 bit and this will be done anyway */
+	lcg_current = LCG_a * lcg_current + LCG_c;
+
+	return(lcg_current);
+}
+
 /********************************************************************
 Tries a search shortcut based on the last insert. */
 UNIV_INLINE
@@ -493,9 +533,13 @@ page_cur_open_on_rnd_user_rec(
 		return;
 	}
 
+	if (srv_use_legacy_cardinality_algorithm) {
 		page_rnd += 87584577;
 
 		rnd = page_rnd % page_get_n_recs(page);
+	} else {
+		rnd = (ulint) page_cur_lcg_prng() % page_get_n_recs(page);
+	}
 
 	rec = page_get_infimum_rec(page);
 
@@ -1437,3 +1481,30 @@ page_cur_delete_rec(
 		page_dir_balance_slot(page, cur_slot_no);
 	}
 }
+
+#ifdef UNIV_COMPILE_TEST_FUNCS
+
+/***********************************************************************
+Print the first n numbers, generated by page_cur_lcg_prng() to make sure
+(visually) that it works properly. */
+void
+test_page_cur_lcg_prng(
+/*===================*/
+	int	n)	/* in: print first n numbers */
+{
+	int			i;
+	unsigned long long	rnd;
+
+	for (i = 0; i < n; i++) {
+		rnd = page_cur_lcg_prng();
+		printf("%llu\t%%2=%llu %%3=%llu %%5=%llu %%7=%llu %%11=%llu\n",
+		       rnd,
+		       rnd % 2,
+		       rnd % 3,
+		       rnd % 5,
+		       rnd % 7,
+		       rnd % 11);
+	}
+}
+
+#endif /* UNIV_COMPILE_TEST_FUNCS */

srv/srv0srv.c

@@ -256,6 +256,12 @@ ulint srv_read_ahead_seq = 0;
 /* variable to count the number of random read-aheads */
 ulint srv_read_ahead_rnd = 0;
 
+/* An option to enable the fix for "Bug#43660 SHOW INDEXES/ANALYZE does
+NOT update cardinality for indexes of InnoDB table". By default we are
+running with the fix disabled because MySQL 5.1 is frozen for such
+behavioral changes. */
+char srv_use_legacy_cardinality_algorithm = TRUE;
+
 /* structure to pass status variables to MySQL */
 export_struc export_vars;