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304 lines
8.0 KiB
C
304 lines
8.0 KiB
C
/*-------------------------------------------------------------------------
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*
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* pgstatapprox.c
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* Bloat estimation functions
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*
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* Copyright (c) 2014-2017, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* contrib/pgstattuple/pgstatapprox.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "access/visibilitymap.h"
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#include "access/transam.h"
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#include "access/xact.h"
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#include "access/multixact.h"
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#include "access/htup_details.h"
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#include "catalog/namespace.h"
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#include "funcapi.h"
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#include "miscadmin.h"
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#include "storage/bufmgr.h"
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#include "storage/freespace.h"
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#include "storage/procarray.h"
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#include "storage/lmgr.h"
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#include "utils/builtins.h"
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#include "utils/tqual.h"
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#include "commands/vacuum.h"
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PG_FUNCTION_INFO_V1(pgstattuple_approx);
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PG_FUNCTION_INFO_V1(pgstattuple_approx_v1_5);
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Datum pgstattuple_approx_internal(Oid relid, FunctionCallInfo fcinfo);
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typedef struct output_type
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{
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uint64 table_len;
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uint64 scanned_percent;
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uint64 tuple_count;
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uint64 tuple_len;
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double tuple_percent;
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uint64 dead_tuple_count;
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uint64 dead_tuple_len;
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double dead_tuple_percent;
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uint64 free_space;
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double free_percent;
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} output_type;
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#define NUM_OUTPUT_COLUMNS 10
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/*
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* This function takes an already open relation and scans its pages,
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* skipping those that have the corresponding visibility map bit set.
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* For pages we skip, we find the free space from the free space map
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* and approximate tuple_len on that basis. For the others, we count
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* the exact number of dead tuples etc.
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*
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* This scan is loosely based on vacuumlazy.c:lazy_scan_heap(), but
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* we do not try to avoid skipping single pages.
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*/
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static void
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statapprox_heap(Relation rel, output_type *stat)
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{
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BlockNumber scanned,
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nblocks,
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blkno;
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Buffer vmbuffer = InvalidBuffer;
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BufferAccessStrategy bstrategy;
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TransactionId OldestXmin;
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uint64 misc_count = 0;
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OldestXmin = GetOldestXmin(rel, true);
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bstrategy = GetAccessStrategy(BAS_BULKREAD);
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nblocks = RelationGetNumberOfBlocks(rel);
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scanned = 0;
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for (blkno = 0; blkno < nblocks; blkno++)
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{
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Buffer buf;
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Page page;
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OffsetNumber offnum,
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maxoff;
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Size freespace;
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CHECK_FOR_INTERRUPTS();
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/*
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* If the page has only visible tuples, then we can find out the free
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* space from the FSM and move on.
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*/
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if (VM_ALL_VISIBLE(rel, blkno, &vmbuffer))
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{
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freespace = GetRecordedFreeSpace(rel, blkno);
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stat->tuple_len += BLCKSZ - freespace;
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stat->free_space += freespace;
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continue;
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}
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buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno,
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RBM_NORMAL, bstrategy);
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LockBuffer(buf, BUFFER_LOCK_SHARE);
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page = BufferGetPage(buf);
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/*
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* It's not safe to call PageGetHeapFreeSpace() on new pages, so we
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* treat them as being free space for our purposes.
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*/
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if (!PageIsNew(page))
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stat->free_space += PageGetHeapFreeSpace(page);
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else
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stat->free_space += BLCKSZ - SizeOfPageHeaderData;
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if (PageIsNew(page) || PageIsEmpty(page))
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{
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UnlockReleaseBuffer(buf);
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continue;
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}
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scanned++;
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/*
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* Look at each tuple on the page and decide whether it's live or
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* dead, then count it and its size. Unlike lazy_scan_heap, we can
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* afford to ignore problems and special cases.
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*/
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maxoff = PageGetMaxOffsetNumber(page);
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for (offnum = FirstOffsetNumber;
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offnum <= maxoff;
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offnum = OffsetNumberNext(offnum))
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{
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ItemId itemid;
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HeapTupleData tuple;
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itemid = PageGetItemId(page, offnum);
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if (!ItemIdIsUsed(itemid) || ItemIdIsRedirected(itemid) ||
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ItemIdIsDead(itemid))
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{
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continue;
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}
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Assert(ItemIdIsNormal(itemid));
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ItemPointerSet(&(tuple.t_self), blkno, offnum);
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tuple.t_data = (HeapTupleHeader) PageGetItem(page, itemid);
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tuple.t_len = ItemIdGetLength(itemid);
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tuple.t_tableOid = RelationGetRelid(rel);
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/*
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* We count live and dead tuples, but we also need to add up
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* others in order to feed vac_estimate_reltuples.
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*/
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switch (HeapTupleSatisfiesVacuum(&tuple, OldestXmin, buf))
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{
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case HEAPTUPLE_RECENTLY_DEAD:
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misc_count++;
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/* Fall through */
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case HEAPTUPLE_DEAD:
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stat->dead_tuple_len += tuple.t_len;
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stat->dead_tuple_count++;
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break;
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case HEAPTUPLE_LIVE:
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stat->tuple_len += tuple.t_len;
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stat->tuple_count++;
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break;
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case HEAPTUPLE_INSERT_IN_PROGRESS:
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case HEAPTUPLE_DELETE_IN_PROGRESS:
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misc_count++;
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break;
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default:
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elog(ERROR, "unexpected HeapTupleSatisfiesVacuum result");
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break;
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}
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}
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UnlockReleaseBuffer(buf);
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}
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stat->table_len = (uint64) nblocks *BLCKSZ;
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stat->tuple_count = vac_estimate_reltuples(rel, false, nblocks, scanned,
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stat->tuple_count + misc_count);
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/*
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* Calculate percentages if the relation has one or more pages.
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*/
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if (nblocks != 0)
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{
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stat->scanned_percent = 100 * scanned / nblocks;
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stat->tuple_percent = 100.0 * stat->tuple_len / stat->table_len;
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stat->dead_tuple_percent = 100.0 * stat->dead_tuple_len / stat->table_len;
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stat->free_percent = 100.0 * stat->free_space / stat->table_len;
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}
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if (BufferIsValid(vmbuffer))
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{
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ReleaseBuffer(vmbuffer);
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vmbuffer = InvalidBuffer;
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}
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}
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/*
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* Returns estimated live/dead tuple statistics for the given relid.
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*
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* The superuser() check here must be kept as the library might be upgraded
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* without the extension being upgraded, meaning that in pre-1.5 installations
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* these functions could be called by any user.
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*/
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Datum
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pgstattuple_approx(PG_FUNCTION_ARGS)
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{
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Oid relid = PG_GETARG_OID(0);
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if (!superuser())
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ereport(ERROR,
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(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
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(errmsg("must be superuser to use pgstattuple functions"))));
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PG_RETURN_DATUM(pgstattuple_approx_internal(relid, fcinfo));
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}
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/*
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* As of pgstattuple version 1.5, we no longer need to check if the user
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* is a superuser because we REVOKE EXECUTE on the SQL function from PUBLIC.
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* Users can then grant access to it based on their policies.
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*
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* Otherwise identical to pgstattuple_approx (above).
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*/
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Datum
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pgstattuple_approx_v1_5(PG_FUNCTION_ARGS)
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{
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Oid relid = PG_GETARG_OID(0);
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PG_RETURN_DATUM(pgstattuple_approx_internal(relid, fcinfo));
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}
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Datum
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pgstattuple_approx_internal(Oid relid, FunctionCallInfo fcinfo)
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{
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Relation rel;
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output_type stat = {0};
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TupleDesc tupdesc;
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bool nulls[NUM_OUTPUT_COLUMNS];
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Datum values[NUM_OUTPUT_COLUMNS];
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HeapTuple ret;
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int i = 0;
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if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
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elog(ERROR, "return type must be a row type");
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if (tupdesc->natts != NUM_OUTPUT_COLUMNS)
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elog(ERROR, "incorrect number of output arguments");
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rel = relation_open(relid, AccessShareLock);
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/*
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* Reject attempts to read non-local temporary relations; we would be
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* likely to get wrong data since we have no visibility into the owning
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* session's local buffers.
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*/
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if (RELATION_IS_OTHER_TEMP(rel))
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ereport(ERROR,
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(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
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errmsg("cannot access temporary tables of other sessions")));
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/*
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* We support only ordinary relations and materialised views, because we
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* depend on the visibility map and free space map for our estimates about
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* unscanned pages.
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*/
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if (!(rel->rd_rel->relkind == RELKIND_RELATION ||
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rel->rd_rel->relkind == RELKIND_MATVIEW))
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ereport(ERROR,
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(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
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errmsg("\"%s\" is not a table or materialized view",
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RelationGetRelationName(rel))));
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statapprox_heap(rel, &stat);
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relation_close(rel, AccessShareLock);
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memset(nulls, 0, sizeof(nulls));
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values[i++] = Int64GetDatum(stat.table_len);
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values[i++] = Float8GetDatum(stat.scanned_percent);
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values[i++] = Int64GetDatum(stat.tuple_count);
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values[i++] = Int64GetDatum(stat.tuple_len);
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values[i++] = Float8GetDatum(stat.tuple_percent);
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values[i++] = Int64GetDatum(stat.dead_tuple_count);
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values[i++] = Int64GetDatum(stat.dead_tuple_len);
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values[i++] = Float8GetDatum(stat.dead_tuple_percent);
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values[i++] = Int64GetDatum(stat.free_space);
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values[i++] = Float8GetDatum(stat.free_percent);
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ret = heap_form_tuple(tupdesc, values, nulls);
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return HeapTupleGetDatum(ret);
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}
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