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analyze.c
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analyze.c
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/*-------------------------------------------------------------------------
*
* analyze.c
* the Postgres statistics generator
*
* Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/commands/analyze.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include <math.h>
#include "access/multixact.h"
#include "access/transam.h"
#include "access/tupconvert.h"
#include "access/tuptoaster.h"
#include "access/visibilitymap.h"
#include "access/xact.h"
#include "catalog/index.h"
#include "catalog/indexing.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_inherits_fn.h"
#include "catalog/pg_namespace.h"
#include "commands/dbcommands.h"
#include "commands/tablecmds.h"
#include "commands/vacuum.h"
#include "executor/executor.h"
#include "foreign/fdwapi.h"
#include "miscadmin.h"
#include "nodes/nodeFuncs.h"
#include "parser/parse_oper.h"
#include "parser/parse_relation.h"
#include "pgstat.h"
#include "postmaster/autovacuum.h"
#include "storage/bufmgr.h"
#include "storage/lmgr.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "utils/acl.h"
#include "utils/attoptcache.h"
#include "utils/datum.h"
#include "utils/guc.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/pg_rusage.h"
#include "utils/sortsupport.h"
#include "utils/syscache.h"
#include "utils/timestamp.h"
#include "utils/tqual.h"
/* Data structure for Algorithm S from Knuth 3.4.2 */
typedef struct
{
BlockNumber N; /* number of blocks, known in advance */
int n; /* desired sample size */
BlockNumber t; /* current block number */
int m; /* blocks selected so far */
} BlockSamplerData;
typedef BlockSamplerData *BlockSampler;
/* Per-index data for ANALYZE */
typedef struct AnlIndexData
{
IndexInfo *indexInfo; /* BuildIndexInfo result */
double tupleFract; /* fraction of rows for partial index */
VacAttrStats **vacattrstats; /* index attrs to analyze */
int attr_cnt;
} AnlIndexData;
/* Default statistics target (GUC parameter) */
int default_statistics_target = 100;
/* A few variables that don't seem worth passing around as parameters */
static MemoryContext anl_context = NULL;
static BufferAccessStrategy vac_strategy;
static void do_analyze_rel(Relation onerel, VacuumStmt *vacstmt,
AcquireSampleRowsFunc acquirefunc, BlockNumber relpages,
bool inh, int elevel);
static void BlockSampler_Init(BlockSampler bs, BlockNumber nblocks,
int samplesize);
static bool BlockSampler_HasMore(BlockSampler bs);
static BlockNumber BlockSampler_Next(BlockSampler bs);
static void compute_index_stats(Relation onerel, double totalrows,
AnlIndexData *indexdata, int nindexes,
HeapTuple *rows, int numrows,
MemoryContext col_context);
static VacAttrStats *examine_attribute(Relation onerel, int attnum,
Node *index_expr);
static int acquire_sample_rows(Relation onerel, int elevel,
HeapTuple *rows, int targrows,
double *totalrows, double *totaldeadrows);
static int compare_rows(const void *a, const void *b);
static int acquire_inherited_sample_rows(Relation onerel, int elevel,
HeapTuple *rows, int targrows,
double *totalrows, double *totaldeadrows);
static void update_attstats(Oid relid, bool inh,
int natts, VacAttrStats **vacattrstats);
static Datum std_fetch_func(VacAttrStatsP stats, int rownum, bool *isNull);
static Datum ind_fetch_func(VacAttrStatsP stats, int rownum, bool *isNull);
/*
* analyze_rel() -- analyze one relation
*/
void
analyze_rel(Oid relid, VacuumStmt *vacstmt, BufferAccessStrategy bstrategy)
{
Relation onerel;
int elevel;
AcquireSampleRowsFunc acquirefunc = NULL;
BlockNumber relpages = 0;
/* Select logging level */
if (vacstmt->options & VACOPT_VERBOSE)
elevel = INFO;
else
elevel = DEBUG2;
/* Set up static variables */
vac_strategy = bstrategy;
/*
* Check for user-requested abort.
*/
CHECK_FOR_INTERRUPTS();
/*
* Open the relation, getting ShareUpdateExclusiveLock to ensure that two
* ANALYZEs don't run on it concurrently. (This also locks out a
* concurrent VACUUM, which doesn't matter much at the moment but might
* matter if we ever try to accumulate stats on dead tuples.) If the rel
* has been dropped since we last saw it, we don't need to process it.
*/
if (!(vacstmt->options & VACOPT_NOWAIT))
onerel = try_relation_open(relid, ShareUpdateExclusiveLock);
else if (ConditionalLockRelationOid(relid, ShareUpdateExclusiveLock))
onerel = try_relation_open(relid, NoLock);
else
{
onerel = NULL;
if (IsAutoVacuumWorkerProcess() && Log_autovacuum_min_duration >= 0)
ereport(LOG,
(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
errmsg("skipping analyze of \"%s\" --- lock not available",
vacstmt->relation->relname)));
}
if (!onerel)
return;
/*
* Check permissions --- this should match vacuum's check!
*/
if (!(pg_class_ownercheck(RelationGetRelid(onerel), GetUserId()) ||
(pg_database_ownercheck(MyDatabaseId, GetUserId()) && !onerel->rd_rel->relisshared)))
{
/* No need for a WARNING if we already complained during VACUUM */
if (!(vacstmt->options & VACOPT_VACUUM))
{
if (onerel->rd_rel->relisshared)
ereport(WARNING,
(errmsg("skipping \"%s\" --- only superuser can analyze it",
RelationGetRelationName(onerel))));
else if (onerel->rd_rel->relnamespace == PG_CATALOG_NAMESPACE)
ereport(WARNING,
(errmsg("skipping \"%s\" --- only superuser or database owner can analyze it",
RelationGetRelationName(onerel))));
else
ereport(WARNING,
(errmsg("skipping \"%s\" --- only table or database owner can analyze it",
RelationGetRelationName(onerel))));
}
relation_close(onerel, ShareUpdateExclusiveLock);
return;
}
/*
* Silently ignore tables that are temp tables of other backends ---
* trying to analyze these is rather pointless, since their contents are
* probably not up-to-date on disk. (We don't throw a warning here; it
* would just lead to chatter during a database-wide ANALYZE.)
*/
if (RELATION_IS_OTHER_TEMP(onerel))
{
relation_close(onerel, ShareUpdateExclusiveLock);
return;
}
/*
* We can ANALYZE any table except pg_statistic. See update_attstats
*/
if (RelationGetRelid(onerel) == StatisticRelationId)
{
relation_close(onerel, ShareUpdateExclusiveLock);
return;
}
/*
* Check that it's a plain table, materialized view, or foreign table; we
* used to do this in get_rel_oids() but seems safer to check after we've
* locked the relation.
*/
if (onerel->rd_rel->relkind == RELKIND_RELATION ||
onerel->rd_rel->relkind == RELKIND_MATVIEW)
{
/* Regular table, so we'll use the regular row acquisition function */
acquirefunc = acquire_sample_rows;
/* Also get regular table's size */
relpages = RelationGetNumberOfBlocks(onerel);
}
else if (onerel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
{
/*
* For a foreign table, call the FDW's hook function to see whether it
* supports analysis.
*/
FdwRoutine *fdwroutine;
bool ok = false;
fdwroutine = GetFdwRoutineByRelId(RelationGetRelid(onerel));
if (fdwroutine->AnalyzeForeignTable != NULL)
ok = fdwroutine->AnalyzeForeignTable(onerel,
&acquirefunc,
&relpages);
if (!ok)
{
ereport(WARNING,
(errmsg("skipping \"%s\" --- cannot analyze this foreign table",
RelationGetRelationName(onerel))));
relation_close(onerel, ShareUpdateExclusiveLock);
return;
}
}
else
{
/* No need for a WARNING if we already complained during VACUUM */
if (!(vacstmt->options & VACOPT_VACUUM))
ereport(WARNING,
(errmsg("skipping \"%s\" --- cannot analyze non-tables or special system tables",
RelationGetRelationName(onerel))));
relation_close(onerel, ShareUpdateExclusiveLock);
return;
}
/*
* OK, let's do it. First let other backends know I'm in ANALYZE.
*/
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
MyPgXact->vacuumFlags |= PROC_IN_ANALYZE;
LWLockRelease(ProcArrayLock);
/*
* Do the normal non-recursive ANALYZE.
*/
do_analyze_rel(onerel, vacstmt, acquirefunc, relpages, false, elevel);
/*
* If there are child tables, do recursive ANALYZE.
*/
if (onerel->rd_rel->relhassubclass)
do_analyze_rel(onerel, vacstmt, acquirefunc, relpages, true, elevel);
/*
* Close source relation now, but keep lock so that no one deletes it
* before we commit. (If someone did, they'd fail to clean up the entries
* we made in pg_statistic. Also, releasing the lock before commit would
* expose us to concurrent-update failures in update_attstats.)
*/
relation_close(onerel, NoLock);
/*
* Reset my PGXACT flag. Note: we need this here, and not in vacuum_rel,
* because the vacuum flag is cleared by the end-of-xact code.
*/
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
MyPgXact->vacuumFlags &= ~PROC_IN_ANALYZE;
LWLockRelease(ProcArrayLock);
}
/*
* do_analyze_rel() -- analyze one relation, recursively or not
*
* Note that "acquirefunc" is only relevant for the non-inherited case.
* If we supported foreign tables in inheritance trees,
* acquire_inherited_sample_rows would need to determine the appropriate
* acquirefunc for each child table.
*/
static void
do_analyze_rel(Relation onerel, VacuumStmt *vacstmt,
AcquireSampleRowsFunc acquirefunc, BlockNumber relpages,
bool inh, int elevel)
{
int attr_cnt,
tcnt,
i,
ind;
Relation *Irel;
int nindexes;
bool hasindex;
VacAttrStats **vacattrstats;
AnlIndexData *indexdata;
int targrows,
numrows;
double totalrows,
totaldeadrows;
HeapTuple *rows;
PGRUsage ru0;
TimestampTz starttime = 0;
MemoryContext caller_context;
Oid save_userid;
int save_sec_context;
int save_nestlevel;
if (inh)
ereport(elevel,
(errmsg("analyzing \"%s.%s\" inheritance tree",
get_namespace_name(RelationGetNamespace(onerel)),
RelationGetRelationName(onerel))));
else
ereport(elevel,
(errmsg("analyzing \"%s.%s\"",
get_namespace_name(RelationGetNamespace(onerel)),
RelationGetRelationName(onerel))));
/*
* Set up a working context so that we can easily free whatever junk gets
* created.
*/
anl_context = AllocSetContextCreate(CurrentMemoryContext,
"Analyze",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
caller_context = MemoryContextSwitchTo(anl_context);
/*
* Switch to the table owner's userid, so that any index functions are run
* as that user. Also lock down security-restricted operations and
* arrange to make GUC variable changes local to this command.
*/
GetUserIdAndSecContext(&save_userid, &save_sec_context);
SetUserIdAndSecContext(onerel->rd_rel->relowner,
save_sec_context | SECURITY_RESTRICTED_OPERATION);
save_nestlevel = NewGUCNestLevel();
/* measure elapsed time iff autovacuum logging requires it */
if (IsAutoVacuumWorkerProcess() && Log_autovacuum_min_duration >= 0)
{
pg_rusage_init(&ru0);
if (Log_autovacuum_min_duration > 0)
starttime = GetCurrentTimestamp();
}
/*
* Determine which columns to analyze
*
* Note that system attributes are never analyzed.
*/
if (vacstmt->va_cols != NIL)
{
ListCell *le;
vacattrstats = (VacAttrStats **) palloc(list_length(vacstmt->va_cols) *
sizeof(VacAttrStats *));
tcnt = 0;
foreach(le, vacstmt->va_cols)
{
char *col = strVal(lfirst(le));
i = attnameAttNum(onerel, col, false);
if (i == InvalidAttrNumber)
ereport(ERROR,
(errcode(ERRCODE_UNDEFINED_COLUMN),
errmsg("column \"%s\" of relation \"%s\" does not exist",
col, RelationGetRelationName(onerel))));
vacattrstats[tcnt] = examine_attribute(onerel, i, NULL);
if (vacattrstats[tcnt] != NULL)
tcnt++;
}
attr_cnt = tcnt;
}
else
{
attr_cnt = onerel->rd_att->natts;
vacattrstats = (VacAttrStats **)
palloc(attr_cnt * sizeof(VacAttrStats *));
tcnt = 0;
for (i = 1; i <= attr_cnt; i++)
{
vacattrstats[tcnt] = examine_attribute(onerel, i, NULL);
if (vacattrstats[tcnt] != NULL)
tcnt++;
}
attr_cnt = tcnt;
}
/*
* Open all indexes of the relation, and see if there are any analyzable
* columns in the indexes. We do not analyze index columns if there was
* an explicit column list in the ANALYZE command, however. If we are
* doing a recursive scan, we don't want to touch the parent's indexes at
* all.
*/
if (!inh)
vac_open_indexes(onerel, AccessShareLock, &nindexes, &Irel);
else
{
Irel = NULL;
nindexes = 0;
}
hasindex = (nindexes > 0);
indexdata = NULL;
if (hasindex)
{
indexdata = (AnlIndexData *) palloc0(nindexes * sizeof(AnlIndexData));
for (ind = 0; ind < nindexes; ind++)
{
AnlIndexData *thisdata = &indexdata[ind];
IndexInfo *indexInfo;
thisdata->indexInfo = indexInfo = BuildIndexInfo(Irel[ind]);
thisdata->tupleFract = 1.0; /* fix later if partial */
if (indexInfo->ii_Expressions != NIL && vacstmt->va_cols == NIL)
{
ListCell *indexpr_item = list_head(indexInfo->ii_Expressions);
thisdata->vacattrstats = (VacAttrStats **)
palloc(indexInfo->ii_NumIndexAttrs * sizeof(VacAttrStats *));
tcnt = 0;
for (i = 0; i < indexInfo->ii_NumIndexAttrs; i++)
{
int keycol = indexInfo->ii_KeyAttrNumbers[i];
if (keycol == 0)
{
/* Found an index expression */
Node *indexkey;
if (indexpr_item == NULL) /* shouldn't happen */
elog(ERROR, "too few entries in indexprs list");
indexkey = (Node *) lfirst(indexpr_item);
indexpr_item = lnext(indexpr_item);
thisdata->vacattrstats[tcnt] =
examine_attribute(Irel[ind], i + 1, indexkey);
if (thisdata->vacattrstats[tcnt] != NULL)
tcnt++;
}
}
thisdata->attr_cnt = tcnt;
}
}
}
/*
* Determine how many rows we need to sample, using the worst case from
* all analyzable columns. We use a lower bound of 100 rows to avoid
* possible overflow in Vitter's algorithm. (Note: that will also be the
* target in the corner case where there are no analyzable columns.)
*/
targrows = 100;
for (i = 0; i < attr_cnt; i++)
{
if (targrows < vacattrstats[i]->minrows)
targrows = vacattrstats[i]->minrows;
}
for (ind = 0; ind < nindexes; ind++)
{
AnlIndexData *thisdata = &indexdata[ind];
for (i = 0; i < thisdata->attr_cnt; i++)
{
if (targrows < thisdata->vacattrstats[i]->minrows)
targrows = thisdata->vacattrstats[i]->minrows;
}
}
/*
* Acquire the sample rows
*/
rows = (HeapTuple *) palloc(targrows * sizeof(HeapTuple));
if (inh)
numrows = acquire_inherited_sample_rows(onerel, elevel,
rows, targrows,
&totalrows, &totaldeadrows);
else
numrows = (*acquirefunc) (onerel, elevel,
rows, targrows,
&totalrows, &totaldeadrows);
/*
* Compute the statistics. Temporary results during the calculations for
* each column are stored in a child context. The calc routines are
* responsible to make sure that whatever they store into the VacAttrStats
* structure is allocated in anl_context.
*/
if (numrows > 0)
{
MemoryContext col_context,
old_context;
col_context = AllocSetContextCreate(anl_context,
"Analyze Column",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
old_context = MemoryContextSwitchTo(col_context);
for (i = 0; i < attr_cnt; i++)
{
VacAttrStats *stats = vacattrstats[i];
AttributeOpts *aopt;
stats->rows = rows;
stats->tupDesc = onerel->rd_att;
(*stats->compute_stats) (stats,
std_fetch_func,
numrows,
totalrows);
/*
* If the appropriate flavor of the n_distinct option is
* specified, override with the corresponding value.
*/
aopt = get_attribute_options(onerel->rd_id, stats->attr->attnum);
if (aopt != NULL)
{
float8 n_distinct;
n_distinct = inh ? aopt->n_distinct_inherited : aopt->n_distinct;
if (n_distinct != 0.0)
stats->stadistinct = n_distinct;
}
MemoryContextResetAndDeleteChildren(col_context);
}
if (hasindex)
compute_index_stats(onerel, totalrows,
indexdata, nindexes,
rows, numrows,
col_context);
MemoryContextSwitchTo(old_context);
MemoryContextDelete(col_context);
/*
* Emit the completed stats rows into pg_statistic, replacing any
* previous statistics for the target columns. (If there are stats in
* pg_statistic for columns we didn't process, we leave them alone.)
*/
update_attstats(RelationGetRelid(onerel), inh,
attr_cnt, vacattrstats);
for (ind = 0; ind < nindexes; ind++)
{
AnlIndexData *thisdata = &indexdata[ind];
update_attstats(RelationGetRelid(Irel[ind]), false,
thisdata->attr_cnt, thisdata->vacattrstats);
}
}
/*
* Update pages/tuples stats in pg_class ... but not if we're doing
* inherited stats.
*/
if (!inh)
vac_update_relstats(onerel,
relpages,
totalrows,
visibilitymap_count(onerel),
hasindex,
InvalidTransactionId,
InvalidMultiXactId);
/*
* Same for indexes. Vacuum always scans all indexes, so if we're part of
* VACUUM ANALYZE, don't overwrite the accurate count already inserted by
* VACUUM.
*/
if (!inh && !(vacstmt->options & VACOPT_VACUUM))
{
for (ind = 0; ind < nindexes; ind++)
{
AnlIndexData *thisdata = &indexdata[ind];
double totalindexrows;
totalindexrows = ceil(thisdata->tupleFract * totalrows);
vac_update_relstats(Irel[ind],
RelationGetNumberOfBlocks(Irel[ind]),
totalindexrows,
0,
false,
InvalidTransactionId,
InvalidMultiXactId);
}
}
/*
* Report ANALYZE to the stats collector, too. However, if doing
* inherited stats we shouldn't report, because the stats collector only
* tracks per-table stats.
*/
if (!inh)
pgstat_report_analyze(onerel, totalrows, totaldeadrows);
/* If this isn't part of VACUUM ANALYZE, let index AMs do cleanup */
if (!(vacstmt->options & VACOPT_VACUUM))
{
for (ind = 0; ind < nindexes; ind++)
{
IndexBulkDeleteResult *stats;
IndexVacuumInfo ivinfo;
ivinfo.index = Irel[ind];
ivinfo.analyze_only = true;
ivinfo.estimated_count = true;
ivinfo.message_level = elevel;
ivinfo.num_heap_tuples = onerel->rd_rel->reltuples;
ivinfo.strategy = vac_strategy;
stats = index_vacuum_cleanup(&ivinfo, NULL);
if (stats)
pfree(stats);
}
}
/* Done with indexes */
vac_close_indexes(nindexes, Irel, NoLock);
/* Log the action if appropriate */
if (IsAutoVacuumWorkerProcess() && Log_autovacuum_min_duration >= 0)
{
if (Log_autovacuum_min_duration == 0 ||
TimestampDifferenceExceeds(starttime, GetCurrentTimestamp(),
Log_autovacuum_min_duration))
ereport(LOG,
(errmsg("automatic analyze of table \"%s.%s.%s\" system usage: %s",
get_database_name(MyDatabaseId),
get_namespace_name(RelationGetNamespace(onerel)),
RelationGetRelationName(onerel),
pg_rusage_show(&ru0))));
}
/* Roll back any GUC changes executed by index functions */
AtEOXact_GUC(false, save_nestlevel);
/* Restore userid and security context */
SetUserIdAndSecContext(save_userid, save_sec_context);
/* Restore current context and release memory */
MemoryContextSwitchTo(caller_context);
MemoryContextDelete(anl_context);
anl_context = NULL;
}
/*
* Compute statistics about indexes of a relation
*/
static void
compute_index_stats(Relation onerel, double totalrows,
AnlIndexData *indexdata, int nindexes,
HeapTuple *rows, int numrows,
MemoryContext col_context)
{
MemoryContext ind_context,
old_context;
Datum values[INDEX_MAX_KEYS];
bool isnull[INDEX_MAX_KEYS];
int ind,
i;
ind_context = AllocSetContextCreate(anl_context,
"Analyze Index",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
old_context = MemoryContextSwitchTo(ind_context);
for (ind = 0; ind < nindexes; ind++)
{
AnlIndexData *thisdata = &indexdata[ind];
IndexInfo *indexInfo = thisdata->indexInfo;
int attr_cnt = thisdata->attr_cnt;
TupleTableSlot *slot;
EState *estate;
ExprContext *econtext;
List *predicate;
Datum *exprvals;
bool *exprnulls;
int numindexrows,
tcnt,
rowno;
double totalindexrows;
/* Ignore index if no columns to analyze and not partial */
if (attr_cnt == 0 && indexInfo->ii_Predicate == NIL)
continue;
/*
* Need an EState for evaluation of index expressions and
* partial-index predicates. Create it in the per-index context to be
* sure it gets cleaned up at the bottom of the loop.
*/
estate = CreateExecutorState();
econtext = GetPerTupleExprContext(estate);
/* Need a slot to hold the current heap tuple, too */
slot = MakeSingleTupleTableSlot(RelationGetDescr(onerel));
/* Arrange for econtext's scan tuple to be the tuple under test */
econtext->ecxt_scantuple = slot;
/* Set up execution state for predicate. */
predicate = (List *)
ExecPrepareExpr((Expr *) indexInfo->ii_Predicate,
estate);
/* Compute and save index expression values */
exprvals = (Datum *) palloc(numrows * attr_cnt * sizeof(Datum));
exprnulls = (bool *) palloc(numrows * attr_cnt * sizeof(bool));
numindexrows = 0;
tcnt = 0;
for (rowno = 0; rowno < numrows; rowno++)
{
HeapTuple heapTuple = rows[rowno];
/*
* Reset the per-tuple context each time, to reclaim any cruft
* left behind by evaluating the predicate or index expressions.
*/
ResetExprContext(econtext);
/* Set up for predicate or expression evaluation */
ExecStoreTuple(heapTuple, slot, InvalidBuffer, false);
/* If index is partial, check predicate */
if (predicate != NIL)
{
if (!ExecQual(predicate, econtext, false))
continue;
}
numindexrows++;
if (attr_cnt > 0)
{
/*
* Evaluate the index row to compute expression values. We
* could do this by hand, but FormIndexDatum is convenient.
*/
FormIndexDatum(indexInfo,
slot,
estate,
values,
isnull);
/*
* Save just the columns we care about. We copy the values
* into ind_context from the estate's per-tuple context.
*/
for (i = 0; i < attr_cnt; i++)
{
VacAttrStats *stats = thisdata->vacattrstats[i];
int attnum = stats->attr->attnum;
if (isnull[attnum - 1])
{
exprvals[tcnt] = (Datum) 0;
exprnulls[tcnt] = true;
}
else
{
exprvals[tcnt] = datumCopy(values[attnum - 1],
stats->attrtype->typbyval,
stats->attrtype->typlen);
exprnulls[tcnt] = false;
}
tcnt++;
}
}
}
/*
* Having counted the number of rows that pass the predicate in the
* sample, we can estimate the total number of rows in the index.
*/
thisdata->tupleFract = (double) numindexrows / (double) numrows;
totalindexrows = ceil(thisdata->tupleFract * totalrows);
/*
* Now we can compute the statistics for the expression columns.
*/
if (numindexrows > 0)
{
MemoryContextSwitchTo(col_context);
for (i = 0; i < attr_cnt; i++)
{
VacAttrStats *stats = thisdata->vacattrstats[i];
AttributeOpts *aopt =
get_attribute_options(stats->attr->attrelid,
stats->attr->attnum);
stats->exprvals = exprvals + i;
stats->exprnulls = exprnulls + i;
stats->rowstride = attr_cnt;
(*stats->compute_stats) (stats,
ind_fetch_func,
numindexrows,
totalindexrows);
/*
* If the n_distinct option is specified, it overrides the
* above computation. For indices, we always use just
* n_distinct, not n_distinct_inherited.
*/
if (aopt != NULL && aopt->n_distinct != 0.0)
stats->stadistinct = aopt->n_distinct;
MemoryContextResetAndDeleteChildren(col_context);
}
}
/* And clean up */
MemoryContextSwitchTo(ind_context);
ExecDropSingleTupleTableSlot(slot);
FreeExecutorState(estate);
MemoryContextResetAndDeleteChildren(ind_context);
}
MemoryContextSwitchTo(old_context);
MemoryContextDelete(ind_context);
}
/*
* examine_attribute -- pre-analysis of a single column
*
* Determine whether the column is analyzable; if so, create and initialize
* a VacAttrStats struct for it. If not, return NULL.
*
* If index_expr isn't NULL, then we're trying to analyze an expression index,
* and index_expr is the expression tree representing the column's data.
*/
static VacAttrStats *
examine_attribute(Relation onerel, int attnum, Node *index_expr)
{
Form_pg_attribute attr = onerel->rd_att->attrs[attnum - 1];
HeapTuple typtuple;
VacAttrStats *stats;
int i;
bool ok;
/* Never analyze dropped columns */
if (attr->attisdropped)
return NULL;
/* Don't analyze column if user has specified not to */
if (attr->attstattarget == 0)
return NULL;
/*
* Create the VacAttrStats struct. Note that we only have a copy of the
* fixed fields of the pg_attribute tuple.
*/
stats = (VacAttrStats *) palloc0(sizeof(VacAttrStats));
stats->attr = (Form_pg_attribute) palloc(ATTRIBUTE_FIXED_PART_SIZE);
memcpy(stats->attr, attr, ATTRIBUTE_FIXED_PART_SIZE);
/*
* When analyzing an expression index, believe the expression tree's type
* not the column datatype --- the latter might be the opckeytype storage
* type of the opclass, which is not interesting for our purposes. (Note:
* if we did anything with non-expression index columns, we'd need to
* figure out where to get the correct type info from, but for now that's
* not a problem.) It's not clear whether anyone will care about the
* typmod, but we store that too just in case.
*/
if (index_expr)
{
stats->attrtypid = exprType(index_expr);
stats->attrtypmod = exprTypmod(index_expr);
}
else
{
stats->attrtypid = attr->atttypid;
stats->attrtypmod = attr->atttypmod;
}
typtuple = SearchSysCacheCopy1(TYPEOID,
ObjectIdGetDatum(stats->attrtypid));
if (!HeapTupleIsValid(typtuple))
elog(ERROR, "cache lookup failed for type %u", stats->attrtypid);
stats->attrtype = (Form_pg_type) GETSTRUCT(typtuple);
stats->anl_context = anl_context;
stats->tupattnum = attnum;
/*
* The fields describing the stats->stavalues[n] element types default to
* the type of the data being analyzed, but the type-specific typanalyze
* function can change them if it wants to store something else.
*/
for (i = 0; i < STATISTIC_NUM_SLOTS; i++)
{
stats->statypid[i] = stats->attrtypid;
stats->statyplen[i] = stats->attrtype->typlen;
stats->statypbyval[i] = stats->attrtype->typbyval;
stats->statypalign[i] = stats->attrtype->typalign;
}
/*
* Call the type-specific typanalyze function. If none is specified, use
* std_typanalyze().
*/
if (OidIsValid(stats->attrtype->typanalyze))
ok = DatumGetBool(OidFunctionCall1(stats->attrtype->typanalyze,
PointerGetDatum(stats)));
else
ok = std_typanalyze(stats);
if (!ok || stats->compute_stats == NULL || stats->minrows <= 0)
{
heap_freetuple(typtuple);
pfree(stats->attr);
pfree(stats);
return NULL;
}
return stats;
}
/*
* BlockSampler_Init -- prepare for random sampling of blocknumbers
*
* BlockSampler is used for stage one of our new two-stage tuple
* sampling mechanism as discussed on pgsql-hackers 2004-04-02 (subject
* "Large DB"). It selects a random sample of samplesize blocks out of
* the nblocks blocks in the table. If the table has less than
* samplesize blocks, all blocks are selected.
*
* Since we know the total number of blocks in advance, we can use the
* straightforward Algorithm S from Knuth 3.4.2, rather than Vitter's
* algorithm.
*/
static void
BlockSampler_Init(BlockSampler bs, BlockNumber nblocks, int samplesize)
{
bs->N = nblocks; /* measured table size */
/*
* If we decide to reduce samplesize for tables that have less or not much
* more than samplesize blocks, here is the place to do it.
*/
bs->n = samplesize;
bs->t = 0; /* blocks scanned so far */
bs->m = 0; /* blocks selected so far */
}
static bool
BlockSampler_HasMore(BlockSampler bs)
{
return (bs->t < bs->N) && (bs->m < bs->n);
}
static BlockNumber
BlockSampler_Next(BlockSampler bs)
{
BlockNumber K = bs->N - bs->t; /* remaining blocks */
int k = bs->n - bs->m; /* blocks still to sample */
double p; /* probability to skip block */
double V; /* random */
Assert(BlockSampler_HasMore(bs)); /* hence K > 0 and k > 0 */
if ((BlockNumber) k >= K)
{
/* need all the rest */
bs->m++;
return bs->t++;
}
/*----------
* It is not obvious that this code matches Knuth's Algorithm S.
* Knuth says to skip the current block with probability 1 - k/K.
* If we are to skip, we should advance t (hence decrease K), and
* repeat the same probabilistic test for the next block. The naive
* implementation thus requires an anl_random_fract() call for each block
* number. But we can reduce this to one anl_random_fract() call per
* selected block, by noting that each time the while-test succeeds,