postgresql/src/include/commands/vacuum.h

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/*-------------------------------------------------------------------------
*
* vacuum.h
* header file for postgres vacuum cleaner and statistics analyzer
*
*
* Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
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* src/include/commands/vacuum.h
*
*-------------------------------------------------------------------------
*/
#ifndef VACUUM_H
#define VACUUM_H
#include "access/htup.h"
#include "catalog/pg_statistic.h"
#include "catalog/pg_type.h"
#include "nodes/parsenodes.h"
#include "storage/buf.h"
#include "storage/lock.h"
#include "utils/relcache.h"
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/*----------
* ANALYZE builds one of these structs for each attribute (column) that is
* to be analyzed. The struct and subsidiary data are in anl_context,
* so they live until the end of the ANALYZE operation.
*
* The type-specific typanalyze function is passed a pointer to this struct
* and must return TRUE to continue analysis, FALSE to skip analysis of this
* column. In the TRUE case it must set the compute_stats and minrows fields,
* and can optionally set extra_data to pass additional info to compute_stats.
* minrows is its request for the minimum number of sample rows to be gathered
* (but note this request might not be honored, eg if there are fewer rows
* than that in the table).
*
* The compute_stats routine will be called after sample rows have been
* gathered. Aside from this struct, it is passed:
* fetchfunc: a function for accessing the column values from the
* sample rows
* samplerows: the number of sample tuples
* totalrows: estimated total number of rows in relation
* The fetchfunc may be called with rownum running from 0 to samplerows-1.
* It returns a Datum and an isNull flag.
*
* compute_stats should set stats_valid TRUE if it is able to compute
* any useful statistics. If it does, the remainder of the struct holds
* the information to be stored in a pg_statistic row for the column. Be
* careful to allocate any pointed-to data in anl_context, which will NOT
* be CurrentMemoryContext when compute_stats is called.
*
* Note: for the moment, all comparisons done for statistical purposes
* should use the database's default collation (DEFAULT_COLLATION_OID).
* This might change in some future release.
*----------
*/
typedef struct VacAttrStats *VacAttrStatsP;
typedef Datum (*AnalyzeAttrFetchFunc) (VacAttrStatsP stats, int rownum,
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bool *isNull);
typedef void (*AnalyzeAttrComputeStatsFunc) (VacAttrStatsP stats,
AnalyzeAttrFetchFunc fetchfunc,
int samplerows,
double totalrows);
typedef struct VacAttrStats
{
/*
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* These fields are set up by the main ANALYZE code before invoking the
* type-specific typanalyze function.
*
* Note: do not assume that the data being analyzed has the same datatype
* shown in attr, ie do not trust attr->atttypid, attlen, etc. This is
* because some index opclasses store a different type than the underlying
* column/expression. Instead use attrtypid, attrtypmod, and attrtype for
* information about the datatype being fed to the typanalyze function.
*/
Form_pg_attribute attr; /* copy of pg_attribute row for column */
Oid attrtypid; /* type of data being analyzed */
int32 attrtypmod; /* typmod of data being analyzed */
Form_pg_type attrtype; /* copy of pg_type row for attrtypid */
MemoryContext anl_context; /* where to save long-lived data */
/*
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* These fields must be filled in by the typanalyze routine, unless it
* returns FALSE.
*/
AnalyzeAttrComputeStatsFunc compute_stats; /* function pointer */
int minrows; /* Minimum # of rows wanted for stats */
void *extra_data; /* for extra type-specific data */
/*
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* These fields are to be filled in by the compute_stats routine. (They
* are initialized to zero when the struct is created.)
*/
bool stats_valid;
float4 stanullfrac; /* fraction of entries that are NULL */
int32 stawidth; /* average width of column values */
float4 stadistinct; /* # distinct values */
int16 stakind[STATISTIC_NUM_SLOTS];
Oid staop[STATISTIC_NUM_SLOTS];
int numnumbers[STATISTIC_NUM_SLOTS];
float4 *stanumbers[STATISTIC_NUM_SLOTS];
int numvalues[STATISTIC_NUM_SLOTS];
Datum *stavalues[STATISTIC_NUM_SLOTS];
/*
* These fields describe the stavalues[n] element types. They will be
* initialized to match attrtypid, but a custom typanalyze function might
* want to store an array of something other than the analyzed column's
* elements. It should then overwrite these fields.
*/
Oid statypid[STATISTIC_NUM_SLOTS];
int16 statyplen[STATISTIC_NUM_SLOTS];
bool statypbyval[STATISTIC_NUM_SLOTS];
char statypalign[STATISTIC_NUM_SLOTS];
/*
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* These fields are private to the main ANALYZE code and should not be
* looked at by type-specific functions.
*/
int tupattnum; /* attribute number within tuples */
HeapTuple *rows; /* access info for std fetch function */
TupleDesc tupDesc;
Datum *exprvals; /* access info for index fetch function */
bool *exprnulls;
int rowstride;
} VacAttrStats;
/*
* Parameters customizing behavior of VACUUM and ANALYZE.
*/
typedef struct VacuumParams
{
int freeze_min_age; /* min freeze age, -1 to use default */
int freeze_table_age; /* age at which to scan whole table */
int multixact_freeze_min_age; /* min multixact freeze age,
* -1 to use default */
int multixact_freeze_table_age; /* multixact age at which to
* scan whole table */
bool is_wraparound; /* force a for-wraparound vacuum */
} VacuumParams;
/* GUC parameters */
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extern PGDLLIMPORT int default_statistics_target; /* PGDLLIMPORT for
* PostGIS */
extern int vacuum_freeze_min_age;
extern int vacuum_freeze_table_age;
extern int vacuum_multixact_freeze_min_age;
extern int vacuum_multixact_freeze_table_age;
/* in commands/vacuum.c */
extern void ExecVacuum(VacuumStmt *vacstmt, bool isTopLevel);
extern void vacuum(int options, RangeVar *relation, Oid relid,
VacuumParams *params, List *va_cols,
BufferAccessStrategy bstrategy, bool isTopLevel);
extern void vac_open_indexes(Relation relation, LOCKMODE lockmode,
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int *nindexes, Relation **Irel);
extern void vac_close_indexes(int nindexes, Relation *Irel, LOCKMODE lockmode);
Fix VACUUM so that it always updates pg_class.reltuples/relpages. When we added the ability for vacuum to skip heap pages by consulting the visibility map, we made it just not update the reltuples/relpages statistics if it skipped any pages. But this could leave us with extremely out-of-date stats for a table that contains any unchanging areas, especially for TOAST tables which never get processed by ANALYZE. In particular this could result in autovacuum making poor decisions about when to process the table, as in recent report from Florian Helmberger. And in general it's a bad idea to not update the stats at all. Instead, use the previous values of reltuples/relpages as an estimate of the tuple density in unvisited pages. This approach results in a "moving average" estimate of reltuples, which should converge to the correct value over multiple VACUUM and ANALYZE cycles even when individual measurements aren't very good. This new method for updating reltuples is used by both VACUUM and ANALYZE, with the result that we no longer need the grotty interconnections that caused ANALYZE to not update the stats depending on what had happened in the parent VACUUM command. Also, fix the logic for skipping all-visible pages during VACUUM so that it looks ahead rather than behind to decide what to do, as per a suggestion from Greg Stark. This eliminates useless scanning of all-visible pages at the start of the relation or just after a not-all-visible page. In particular, the first few pages of the relation will not be invariably included in the scanned pages, which seems to help in not overweighting them in the reltuples estimate. Back-patch to 8.4, where the visibility map was introduced.
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extern double vac_estimate_reltuples(Relation relation, bool is_analyze,
BlockNumber total_pages,
BlockNumber scanned_pages,
double scanned_tuples);
extern void vac_update_relstats(Relation relation,
BlockNumber num_pages,
double num_tuples,
BlockNumber num_all_visible_pages,
bool hasindex,
Improve concurrency of foreign key locking This patch introduces two additional lock modes for tuples: "SELECT FOR KEY SHARE" and "SELECT FOR NO KEY UPDATE". These don't block each other, in contrast with already existing "SELECT FOR SHARE" and "SELECT FOR UPDATE". UPDATE commands that do not modify the values stored in the columns that are part of the key of the tuple now grab a SELECT FOR NO KEY UPDATE lock on the tuple, allowing them to proceed concurrently with tuple locks of the FOR KEY SHARE variety. Foreign key triggers now use FOR KEY SHARE instead of FOR SHARE; this means the concurrency improvement applies to them, which is the whole point of this patch. The added tuple lock semantics require some rejiggering of the multixact module, so that the locking level that each transaction is holding can be stored alongside its Xid. Also, multixacts now need to persist across server restarts and crashes, because they can now represent not only tuple locks, but also tuple updates. This means we need more careful tracking of lifetime of pg_multixact SLRU files; since they now persist longer, we require more infrastructure to figure out when they can be removed. pg_upgrade also needs to be careful to copy pg_multixact files over from the old server to the new, or at least part of multixact.c state, depending on the versions of the old and new servers. Tuple time qualification rules (HeapTupleSatisfies routines) need to be careful not to consider tuples with the "is multi" infomask bit set as being only locked; they might need to look up MultiXact values (i.e. possibly do pg_multixact I/O) to find out the Xid that updated a tuple, whereas they previously were assured to only use information readily available from the tuple header. This is considered acceptable, because the extra I/O would involve cases that would previously cause some commands to block waiting for concurrent transactions to finish. Another important change is the fact that locking tuples that have previously been updated causes the future versions to be marked as locked, too; this is essential for correctness of foreign key checks. This causes additional WAL-logging, also (there was previously a single WAL record for a locked tuple; now there are as many as updated copies of the tuple there exist.) With all this in place, contention related to tuples being checked by foreign key rules should be much reduced. As a bonus, the old behavior that a subtransaction grabbing a stronger tuple lock than the parent (sub)transaction held on a given tuple and later aborting caused the weaker lock to be lost, has been fixed. Many new spec files were added for isolation tester framework, to ensure overall behavior is sane. There's probably room for several more tests. There were several reviewers of this patch; in particular, Noah Misch and Andres Freund spent considerable time in it. Original idea for the patch came from Simon Riggs, after a problem report by Joel Jacobson. Most code is from me, with contributions from Marti Raudsepp, Alexander Shulgin, Noah Misch and Andres Freund. This patch was discussed in several pgsql-hackers threads; the most important start at the following message-ids: AANLkTimo9XVcEzfiBR-ut3KVNDkjm2Vxh+t8kAmWjPuv@mail.gmail.com 1290721684-sup-3951@alvh.no-ip.org 1294953201-sup-2099@alvh.no-ip.org 1320343602-sup-2290@alvh.no-ip.org 1339690386-sup-8927@alvh.no-ip.org 4FE5FF020200002500048A3D@gw.wicourts.gov 4FEAB90A0200002500048B7D@gw.wicourts.gov
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TransactionId frozenxid,
MultiXactId minmulti,
bool in_outer_xact);
extern void vacuum_set_xid_limits(Relation rel,
int freeze_min_age, int freeze_table_age,
int multixact_freeze_min_age,
int multixact_freeze_table_age,
TransactionId *oldestXmin,
TransactionId *freezeLimit,
TransactionId *xidFullScanLimit,
MultiXactId *multiXactCutoff,
MultiXactId *mxactFullScanLimit);
extern void vac_update_datfrozenxid(void);
extern void vacuum_delay_point(void);
/* in commands/vacuumlazy.c */
extern void lazy_vacuum_rel(Relation onerel, int options,
VacuumParams *params, BufferAccessStrategy bstrategy);
/* in commands/analyze.c */
extern void analyze_rel(Oid relid, RangeVar *relation, int options,
List *va_cols, bool in_outer_xact,
BufferAccessStrategy bstrategy);
extern bool std_typanalyze(VacAttrStats *stats);
extern double anl_random_fract(void);
extern double anl_init_selection_state(int n);
extern double anl_get_next_S(double t, int n, double *stateptr);
#endif /* VACUUM_H */