From d8e38a78857006189a149acc5b36df3d77fe1e40 Mon Sep 17 00:00:00 2001 From: Ilia Evdokimov Date: Fri, 3 Jan 2025 16:32:43 +0300 Subject: [PATCH] Define macros for minimum rows of stats in ANALYZE This introduces two macros, STATS_MIN_ROWS and EXT_STATS_MIN_ROWS, to represent the default minimum number of rows sampled in ANALYZE. STATS_MIN_ROWS is used for single-column statistics, while EXT_STATS_MIN_ROWS is intended for extended statistics. Both macros replace the hardcoded value of 300, improving clarity. --- src/backend/commands/analyze.c | 26 +++---------------- src/backend/statistics/extended_stats.c | 2 +- src/backend/tsearch/ts_typanalyze.c | 5 ++-- src/backend/utils/adt/rangetypes_typanalyze.c | 5 ++-- .../statistics/extended_stats_internal.h | 11 ++++++++ src/include/statistics/statistics.h | 23 ++++++++++++++++ 6 files changed, 45 insertions(+), 27 deletions(-) diff --git a/src/backend/commands/analyze.c b/src/backend/commands/analyze.c index 2a7769b1fd..4c02e4f18a 100644 --- a/src/backend/commands/analyze.c +++ b/src/backend/commands/analyze.c @@ -1897,40 +1897,22 @@ std_typanalyze(VacAttrStats *stats) { /* Seems to be a scalar datatype */ stats->compute_stats = compute_scalar_stats; - /*-------------------- - * The following choice of minrows is based on the paper - * "Random sampling for histogram construction: how much is enough?" - * by Surajit Chaudhuri, Rajeev Motwani and Vivek Narasayya, in - * Proceedings of ACM SIGMOD International Conference on Management - * of Data, 1998, Pages 436-447. Their Corollary 1 to Theorem 5 - * says that for table size n, histogram size k, maximum relative - * error in bin size f, and error probability gamma, the minimum - * random sample size is - * r = 4 * k * ln(2*n/gamma) / f^2 - * Taking f = 0.5, gamma = 0.01, n = 10^6 rows, we obtain - * r = 305.82 * k - * Note that because of the log function, the dependence on n is - * quite weak; even at n = 10^12, a 300*k sample gives <= 0.66 - * bin size error with probability 0.99. So there's no real need to - * scale for n, which is a good thing because we don't necessarily - * know it at this point. - *-------------------- - */ - stats->minrows = 300 * stats->attstattarget; + /* see comment about the choice of minrows in statistics/statistics.h */ + stats->minrows = (STATS_MIN_ROWS * stats->attstattarget); } else if (OidIsValid(eqopr)) { /* We can still recognize distinct values */ stats->compute_stats = compute_distinct_stats; /* Might as well use the same minrows as above */ - stats->minrows = 300 * stats->attstattarget; + stats->minrows = (STATS_MIN_ROWS * stats->attstattarget); } else { /* Can't do much but the trivial stuff */ stats->compute_stats = compute_trivial_stats; /* Might as well use the same minrows as above */ - stats->minrows = 300 * stats->attstattarget; + stats->minrows = (STATS_MIN_ROWS * stats->attstattarget); } return true; diff --git a/src/backend/statistics/extended_stats.c b/src/backend/statistics/extended_stats.c index aeec3ece41..05f3dd7fbf 100644 --- a/src/backend/statistics/extended_stats.c +++ b/src/backend/statistics/extended_stats.c @@ -317,7 +317,7 @@ ComputeExtStatisticsRows(Relation onerel, MemoryContextDelete(cxt); /* compute sample size based on the statistics target */ - return (300 * result); + return (EXT_STATS_MIN_ROWS * result); } /* diff --git a/src/backend/tsearch/ts_typanalyze.c b/src/backend/tsearch/ts_typanalyze.c index 1494da1c9d..e20e114335 100644 --- a/src/backend/tsearch/ts_typanalyze.c +++ b/src/backend/tsearch/ts_typanalyze.c @@ -17,6 +17,7 @@ #include "catalog/pg_operator.h" #include "commands/vacuum.h" #include "common/hashfn.h" +#include "statistics/statistics.h" #include "tsearch/ts_type.h" #include "utils/builtins.h" #include "varatt.h" @@ -64,8 +65,8 @@ ts_typanalyze(PG_FUNCTION_ARGS) stats->attstattarget = default_statistics_target; stats->compute_stats = compute_tsvector_stats; - /* see comment about the choice of minrows in commands/analyze.c */ - stats->minrows = 300 * stats->attstattarget; + /* see comment about the choice of minrows in statistics/statistics.h */ + stats->minrows = (STATS_MIN_ROWS * stats->attstattarget); PG_RETURN_BOOL(true); } diff --git a/src/backend/utils/adt/rangetypes_typanalyze.c b/src/backend/utils/adt/rangetypes_typanalyze.c index 9dc73af199..a78012ed89 100644 --- a/src/backend/utils/adt/rangetypes_typanalyze.c +++ b/src/backend/utils/adt/rangetypes_typanalyze.c @@ -26,6 +26,7 @@ #include "catalog/pg_operator.h" #include "commands/vacuum.h" +#include "statistics/statistics.h" #include "utils/float.h" #include "utils/fmgrprotos.h" #include "utils/lsyscache.h" @@ -57,7 +58,7 @@ range_typanalyze(PG_FUNCTION_ARGS) stats->compute_stats = compute_range_stats; stats->extra_data = typcache; /* same as in std_typanalyze */ - stats->minrows = 300 * stats->attstattarget; + stats->minrows = (STATS_MIN_ROWS * stats->attstattarget); PG_RETURN_BOOL(true); } @@ -83,7 +84,7 @@ multirange_typanalyze(PG_FUNCTION_ARGS) stats->compute_stats = compute_range_stats; stats->extra_data = typcache; /* same as in std_typanalyze */ - stats->minrows = 300 * stats->attstattarget; + stats->minrows = (STATS_MIN_ROWS * stats->attstattarget); PG_RETURN_BOOL(true); } diff --git a/src/include/statistics/extended_stats_internal.h b/src/include/statistics/extended_stats_internal.h index efcb7dc354..981211186a 100644 --- a/src/include/statistics/extended_stats_internal.h +++ b/src/include/statistics/extended_stats_internal.h @@ -17,6 +17,17 @@ #include "statistics/statistics.h" #include "utils/sortsupport.h" +/* Minimum of rows wanted for extended stats + * + * Based on research, a fixed size proportional to statistics_target + * (300 * statistics_target) is generally sufficient for accurate single-column + * histograms and MCV lists. Its suitability for extended statistics. + * + * XXX While this value works reasonably well for individual columns, its + * suitability for extended statistics is still an open question. + */ +#define EXT_STATS_MIN_ROWS STATS_MIN_ROWS + typedef struct { Oid eqopr; /* '=' operator for datatype, if any */ diff --git a/src/include/statistics/statistics.h b/src/include/statistics/statistics.h index 7dd0f97554..0863e029b1 100644 --- a/src/include/statistics/statistics.h +++ b/src/include/statistics/statistics.h @@ -22,6 +22,29 @@ #define STATS_NDISTINCT_MAGIC 0xA352BFA4 /* struct identifier */ #define STATS_NDISTINCT_TYPE_BASIC 1 /* struct version */ +/*-------------------- + * Minimum of rows wanted for stats + * + * The following choice of minrows is based on the paper + * "Random sampling for histogram construction: how much is enough?" + * by Surajit Chaudhuri, Rajeev Motwani and Vivek Narasayya, in + * Proceedings of ACM SIGMOD International Conference on Management + * of Data, 1998, Pages 436-447. Their Corollary 1 to Theorem 5 + * says that for table size n, histogram size k, maximum relative + * error in bin size f, and error probability gamma, the minimum + * random sample size is + * r = 4 * k * ln(2*n/gamma) / f^2 + * Taking f = 0.5, gamma = 0.01, n = 10^6 rows, we obtain + * r = 305.82 * k + * Note that because of the log function, the dependence on n is + * quite weak; even at n = 10^12, a 300*k sample gives <= 0.66 + * bin size error with probability 0.99. So there's no real need to + * scale for n, which is a good thing because we don't necessarily + * know it at this point. + *-------------------- + */ +#define STATS_MIN_ROWS 300 + /* MVNDistinctItem represents a single combination of columns */ typedef struct MVNDistinctItem { -- 2.34.1