postgresql/contrib/pgstattuple/pgstatapprox.c

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2023-05-09 21:11:15 +00:00
/*-------------------------------------------------------------------------
*
* pgstatapprox.c
* Bloat estimation functions
*
* Copyright (c) 2014-2022, PostgreSQL Global Development Group
*
* IDENTIFICATION
* contrib/pgstattuple/pgstatapprox.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/multixact.h"
#include "access/relation.h"
#include "access/transam.h"
#include "access/visibilitymap.h"
#include "access/xact.h"
#include "catalog/namespace.h"
#include "catalog/pg_am_d.h"
#include "commands/vacuum.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "storage/bufmgr.h"
#include "storage/freespace.h"
#include "storage/lmgr.h"
#include "storage/procarray.h"
#include "utils/builtins.h"
PG_FUNCTION_INFO_V1(pgstattuple_approx);
PG_FUNCTION_INFO_V1(pgstattuple_approx_v1_5);
Datum pgstattuple_approx_internal(Oid relid, FunctionCallInfo fcinfo);
typedef struct output_type
{
uint64 table_len;
uint64 scanned_percent;
uint64 tuple_count;
uint64 tuple_len;
double tuple_percent;
uint64 dead_tuple_count;
uint64 dead_tuple_len;
double dead_tuple_percent;
uint64 free_space;
double free_percent;
} output_type;
#define NUM_OUTPUT_COLUMNS 10
/*
* This function takes an already open relation and scans its pages,
* skipping those that have the corresponding visibility map bit set.
* For pages we skip, we find the free space from the free space map
* and approximate tuple_len on that basis. For the others, we count
* the exact number of dead tuples etc.
*
* This scan is loosely based on vacuumlazy.c:lazy_scan_heap(), but
* we do not try to avoid skipping single pages.
*/
static void
statapprox_heap(Relation rel, output_type *stat)
{
BlockNumber scanned,
nblocks,
blkno;
Buffer vmbuffer = InvalidBuffer;
BufferAccessStrategy bstrategy;
TransactionId OldestXmin;
OldestXmin = GetOldestNonRemovableTransactionId(rel);
bstrategy = GetAccessStrategy(BAS_BULKREAD);
nblocks = RelationGetNumberOfBlocks(rel);
scanned = 0;
for (blkno = 0; blkno < nblocks; blkno++)
{
Buffer buf;
Page page;
OffsetNumber offnum,
maxoff;
Size freespace;
CHECK_FOR_INTERRUPTS();
/*
* If the page has only visible tuples, then we can find out the free
* space from the FSM and move on.
*/
if (VM_ALL_VISIBLE(rel, blkno, &vmbuffer))
{
freespace = GetRecordedFreeSpace(rel, blkno);
stat->tuple_len += BLCKSZ - freespace;
stat->free_space += freespace;
continue;
}
buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno,
RBM_NORMAL, bstrategy);
LockBuffer(buf, BUFFER_LOCK_SHARE);
page = BufferGetPage(buf);
/*
* It's not safe to call PageGetHeapFreeSpace() on new pages, so we
* treat them as being free space for our purposes.
*/
if (!PageIsNew(page))
stat->free_space += PageGetHeapFreeSpace(page);
else
stat->free_space += BLCKSZ - SizeOfPageHeaderData;
/* We may count the page as scanned even if it's new/empty */
scanned++;
if (PageIsNew(page) || PageIsEmpty(page))
{
UnlockReleaseBuffer(buf);
continue;
}
/*
* Look at each tuple on the page and decide whether it's live or
* dead, then count it and its size. Unlike lazy_scan_heap, we can
* afford to ignore problems and special cases.
*/
maxoff = PageGetMaxOffsetNumber(page);
for (offnum = FirstOffsetNumber;
offnum <= maxoff;
offnum = OffsetNumberNext(offnum))
{
ItemId itemid;
HeapTupleData tuple;
itemid = PageGetItemId(page, offnum);
if (!ItemIdIsUsed(itemid) || ItemIdIsRedirected(itemid) ||
ItemIdIsDead(itemid))
{
continue;
}
Assert(ItemIdIsNormal(itemid));
ItemPointerSet(&(tuple.t_self), blkno, offnum);
tuple.t_data = (HeapTupleHeader) PageGetItem(page, itemid);
tuple.t_len = ItemIdGetLength(itemid);
tuple.t_tableOid = RelationGetRelid(rel);
/*
* We follow VACUUM's lead in counting INSERT_IN_PROGRESS tuples
* as "dead" while DELETE_IN_PROGRESS tuples are "live". We don't
* bother distinguishing tuples inserted/deleted by our own
* transaction.
*/
switch (HeapTupleSatisfiesVacuum(&tuple, OldestXmin, buf))
{
case HEAPTUPLE_LIVE:
case HEAPTUPLE_DELETE_IN_PROGRESS:
stat->tuple_len += tuple.t_len;
stat->tuple_count++;
break;
case HEAPTUPLE_DEAD:
case HEAPTUPLE_RECENTLY_DEAD:
case HEAPTUPLE_INSERT_IN_PROGRESS:
stat->dead_tuple_len += tuple.t_len;
stat->dead_tuple_count++;
break;
default:
elog(ERROR, "unexpected HeapTupleSatisfiesVacuum result");
break;
}
}
UnlockReleaseBuffer(buf);
}
stat->table_len = (uint64) nblocks * BLCKSZ;
/*
* We don't know how many tuples are in the pages we didn't scan, so
* extrapolate the live-tuple count to the whole table in the same way
* that VACUUM does. (Like VACUUM, we're not taking a random sample, so
* just extrapolating linearly seems unsafe.) There should be no dead
* tuples in all-visible pages, so no correction is needed for that, and
* we already accounted for the space in those pages, too.
*/
stat->tuple_count = vac_estimate_reltuples(rel, nblocks, scanned,
stat->tuple_count);
/* It's not clear if we could get -1 here, but be safe. */
stat->tuple_count = Max(stat->tuple_count, 0);
/*
* Calculate percentages if the relation has one or more pages.
*/
if (nblocks != 0)
{
stat->scanned_percent = 100 * scanned / nblocks;
stat->tuple_percent = 100.0 * stat->tuple_len / stat->table_len;
stat->dead_tuple_percent = 100.0 * stat->dead_tuple_len / stat->table_len;
stat->free_percent = 100.0 * stat->free_space / stat->table_len;
}
if (BufferIsValid(vmbuffer))
{
ReleaseBuffer(vmbuffer);
vmbuffer = InvalidBuffer;
}
}
/*
* Returns estimated live/dead tuple statistics for the given relid.
*
* The superuser() check here must be kept as the library might be upgraded
* without the extension being upgraded, meaning that in pre-1.5 installations
* these functions could be called by any user.
*/
Datum
pgstattuple_approx(PG_FUNCTION_ARGS)
{
Oid relid = PG_GETARG_OID(0);
if (!superuser())
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("must be superuser to use pgstattuple functions")));
PG_RETURN_DATUM(pgstattuple_approx_internal(relid, fcinfo));
}
/*
* As of pgstattuple version 1.5, we no longer need to check if the user
* is a superuser because we REVOKE EXECUTE on the SQL function from PUBLIC.
* Users can then grant access to it based on their policies.
*
* Otherwise identical to pgstattuple_approx (above).
*/
Datum
pgstattuple_approx_v1_5(PG_FUNCTION_ARGS)
{
Oid relid = PG_GETARG_OID(0);
PG_RETURN_DATUM(pgstattuple_approx_internal(relid, fcinfo));
}
Datum
pgstattuple_approx_internal(Oid relid, FunctionCallInfo fcinfo)
{
Relation rel;
output_type stat = {0};
TupleDesc tupdesc;
bool nulls[NUM_OUTPUT_COLUMNS];
Datum values[NUM_OUTPUT_COLUMNS];
HeapTuple ret;
int i = 0;
if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
elog(ERROR, "return type must be a row type");
if (tupdesc->natts != NUM_OUTPUT_COLUMNS)
elog(ERROR, "incorrect number of output arguments");
rel = relation_open(relid, AccessShareLock);
/*
* Reject attempts to read non-local temporary relations; we would be
* likely to get wrong data since we have no visibility into the owning
* session's local buffers.
*/
if (RELATION_IS_OTHER_TEMP(rel))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot access temporary tables of other sessions")));
/*
* We support only relation kinds with a visibility map and a free space
* map.
*/
if (!(rel->rd_rel->relkind == RELKIND_RELATION ||
rel->rd_rel->relkind == RELKIND_MATVIEW ||
rel->rd_rel->relkind == RELKIND_TOASTVALUE))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("relation \"%s\" is of wrong relation kind",
RelationGetRelationName(rel)),
errdetail_relkind_not_supported(rel->rd_rel->relkind)));
if (rel->rd_rel->relam != HEAP_TABLE_AM_OID)
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("only heap AM is supported")));
statapprox_heap(rel, &stat);
relation_close(rel, AccessShareLock);
memset(nulls, 0, sizeof(nulls));
values[i++] = Int64GetDatum(stat.table_len);
values[i++] = Float8GetDatum(stat.scanned_percent);
values[i++] = Int64GetDatum(stat.tuple_count);
values[i++] = Int64GetDatum(stat.tuple_len);
values[i++] = Float8GetDatum(stat.tuple_percent);
values[i++] = Int64GetDatum(stat.dead_tuple_count);
values[i++] = Int64GetDatum(stat.dead_tuple_len);
values[i++] = Float8GetDatum(stat.dead_tuple_percent);
values[i++] = Int64GetDatum(stat.free_space);
values[i++] = Float8GetDatum(stat.free_percent);
ret = heap_form_tuple(tupdesc, values, nulls);
return HeapTupleGetDatum(ret);
}