650 lines
20 KiB
C
650 lines
20 KiB
C
/*----------------------------------------------------------------------
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*
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* tableam.c
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* Table access method routines too big to be inline functions.
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*
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* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* src/backend/access/table/tableam.c
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*
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* NOTES
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* Note that most function in here are documented in tableam.h, rather than
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* here. That's because there's a lot of inline functions in tableam.h and
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* it'd be harder to understand if one constantly had to switch between files.
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*
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*----------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include <math.h>
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#include "access/heapam.h" /* for ss_* */
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#include "access/tableam.h"
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#include "access/xact.h"
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#include "optimizer/plancat.h"
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#include "storage/bufmgr.h"
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#include "storage/shmem.h"
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#include "storage/smgr.h"
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/* GUC variables */
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char *default_table_access_method = DEFAULT_TABLE_ACCESS_METHOD;
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bool synchronize_seqscans = true;
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/* ----------------------------------------------------------------------------
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* Slot functions.
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* ----------------------------------------------------------------------------
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*/
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const TupleTableSlotOps *
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table_slot_callbacks(Relation relation)
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{
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const TupleTableSlotOps *tts_cb;
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if (relation->rd_tableam)
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tts_cb = relation->rd_tableam->slot_callbacks(relation);
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else if (relation->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
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{
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/*
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* Historically FDWs expect to store heap tuples in slots. Continue
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* handing them one, to make it less painful to adapt FDWs to new
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* versions. The cost of a heap slot over a virtual slot is pretty
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* small.
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*/
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tts_cb = &TTSOpsHeapTuple;
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}
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else
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{
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/*
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* These need to be supported, as some parts of the code (like COPY)
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* need to create slots for such relations too. It seems better to
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* centralize the knowledge that a heap slot is the right thing in
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* that case here.
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*/
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Assert(relation->rd_rel->relkind == RELKIND_VIEW ||
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relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE);
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tts_cb = &TTSOpsVirtual;
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}
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return tts_cb;
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}
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TupleTableSlot *
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table_slot_create(Relation relation, List **reglist)
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{
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const TupleTableSlotOps *tts_cb;
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TupleTableSlot *slot;
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tts_cb = table_slot_callbacks(relation);
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slot = MakeSingleTupleTableSlot(RelationGetDescr(relation), tts_cb);
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if (reglist)
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*reglist = lappend(*reglist, slot);
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return slot;
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}
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/* ----------------------------------------------------------------------------
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* Table scan functions.
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* ----------------------------------------------------------------------------
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*/
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TableScanDesc
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table_beginscan_catalog(Relation relation, int nkeys, struct ScanKeyData *key)
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{
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uint32 flags = SO_TYPE_SEQSCAN |
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SO_ALLOW_STRAT | SO_ALLOW_SYNC | SO_ALLOW_PAGEMODE | SO_TEMP_SNAPSHOT;
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Oid relid = RelationGetRelid(relation);
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Snapshot snapshot = RegisterSnapshot(GetCatalogSnapshot(relid));
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return relation->rd_tableam->scan_begin(relation, snapshot, nkeys, key,
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NULL, flags);
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}
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void
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table_scan_update_snapshot(TableScanDesc scan, Snapshot snapshot)
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{
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Assert(IsMVCCSnapshot(snapshot));
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RegisterSnapshot(snapshot);
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scan->rs_snapshot = snapshot;
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scan->rs_flags |= SO_TEMP_SNAPSHOT;
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}
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/* ----------------------------------------------------------------------------
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* Parallel table scan related functions.
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* ----------------------------------------------------------------------------
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*/
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Size
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table_parallelscan_estimate(Relation rel, Snapshot snapshot)
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{
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Size sz = 0;
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if (IsMVCCSnapshot(snapshot))
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sz = add_size(sz, EstimateSnapshotSpace(snapshot));
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else
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Assert(snapshot == SnapshotAny);
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sz = add_size(sz, rel->rd_tableam->parallelscan_estimate(rel));
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return sz;
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}
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void
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table_parallelscan_initialize(Relation rel, ParallelTableScanDesc pscan,
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Snapshot snapshot)
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{
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Size snapshot_off = rel->rd_tableam->parallelscan_initialize(rel, pscan);
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pscan->phs_snapshot_off = snapshot_off;
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if (IsMVCCSnapshot(snapshot))
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{
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SerializeSnapshot(snapshot, (char *) pscan + pscan->phs_snapshot_off);
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pscan->phs_snapshot_any = false;
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}
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else
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{
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Assert(snapshot == SnapshotAny);
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pscan->phs_snapshot_any = true;
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}
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}
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TableScanDesc
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table_beginscan_parallel(Relation relation, ParallelTableScanDesc parallel_scan)
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{
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Snapshot snapshot;
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uint32 flags = SO_TYPE_SEQSCAN |
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SO_ALLOW_STRAT | SO_ALLOW_SYNC | SO_ALLOW_PAGEMODE;
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Assert(RelationGetRelid(relation) == parallel_scan->phs_relid);
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if (!parallel_scan->phs_snapshot_any)
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{
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/* Snapshot was serialized -- restore it */
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snapshot = RestoreSnapshot((char *) parallel_scan +
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parallel_scan->phs_snapshot_off);
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RegisterSnapshot(snapshot);
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flags |= SO_TEMP_SNAPSHOT;
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}
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else
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{
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/* SnapshotAny passed by caller (not serialized) */
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snapshot = SnapshotAny;
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}
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return relation->rd_tableam->scan_begin(relation, snapshot, 0, NULL,
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parallel_scan, flags);
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}
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/* ----------------------------------------------------------------------------
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* Index scan related functions.
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* ----------------------------------------------------------------------------
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*/
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/*
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* To perform that check simply start an index scan, create the necessary
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* slot, do the heap lookup, and shut everything down again. This could be
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* optimized, but is unlikely to matter from a performance POV. If there
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* frequently are live index pointers also matching a unique index key, the
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* CPU overhead of this routine is unlikely to matter.
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*/
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bool
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table_index_fetch_tuple_check(Relation rel,
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ItemPointer tid,
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Snapshot snapshot,
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bool *all_dead)
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{
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IndexFetchTableData *scan;
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TupleTableSlot *slot;
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bool call_again = false;
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bool found;
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slot = table_slot_create(rel, NULL);
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scan = table_index_fetch_begin(rel);
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found = table_index_fetch_tuple(scan, tid, snapshot, slot, &call_again,
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all_dead);
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table_index_fetch_end(scan);
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ExecDropSingleTupleTableSlot(slot);
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return found;
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}
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/* ------------------------------------------------------------------------
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* Functions for non-modifying operations on individual tuples
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* ------------------------------------------------------------------------
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*/
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void
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table_tuple_get_latest_tid(TableScanDesc scan, ItemPointer tid)
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{
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Relation rel = scan->rs_rd;
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const TableAmRoutine *tableam = rel->rd_tableam;
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/*
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* Since this can be called with user-supplied TID, don't trust the input
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* too much.
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*/
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if (!tableam->tuple_tid_valid(scan, tid))
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ereport(ERROR,
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(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
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errmsg("tid (%u, %u) is not valid for relation \"%s\"",
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ItemPointerGetBlockNumberNoCheck(tid),
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ItemPointerGetOffsetNumberNoCheck(tid),
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RelationGetRelationName(rel))));
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tableam->tuple_get_latest_tid(scan, tid);
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}
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/* ----------------------------------------------------------------------------
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* Functions to make modifications a bit simpler.
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* ----------------------------------------------------------------------------
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*/
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/*
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* simple_table_tuple_insert - insert a tuple
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*
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* Currently, this routine differs from table_tuple_insert only in supplying a
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* default command ID and not allowing access to the speedup options.
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*/
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void
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simple_table_tuple_insert(Relation rel, TupleTableSlot *slot)
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{
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table_tuple_insert(rel, slot, GetCurrentCommandId(true), 0, NULL);
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}
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/*
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* simple_table_tuple_delete - delete a tuple
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*
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* This routine may be used to delete a tuple when concurrent updates of
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* the target tuple are not expected (for example, because we have a lock
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* on the relation associated with the tuple). Any failure is reported
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* via ereport().
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*/
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void
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simple_table_tuple_delete(Relation rel, ItemPointer tid, Snapshot snapshot)
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{
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TM_Result result;
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TM_FailureData tmfd;
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result = table_tuple_delete(rel, tid,
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GetCurrentCommandId(true),
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snapshot, InvalidSnapshot,
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true /* wait for commit */ ,
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&tmfd, false /* changingPart */ );
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switch (result)
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{
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case TM_SelfModified:
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/* Tuple was already updated in current command? */
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elog(ERROR, "tuple already updated by self");
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break;
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case TM_Ok:
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/* done successfully */
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break;
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case TM_Updated:
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elog(ERROR, "tuple concurrently updated");
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break;
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case TM_Deleted:
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elog(ERROR, "tuple concurrently deleted");
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break;
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default:
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elog(ERROR, "unrecognized table_tuple_delete status: %u", result);
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break;
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}
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}
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/*
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* simple_table_tuple_update - replace a tuple
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*
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* This routine may be used to update a tuple when concurrent updates of
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* the target tuple are not expected (for example, because we have a lock
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* on the relation associated with the tuple). Any failure is reported
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* via ereport().
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*/
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void
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simple_table_tuple_update(Relation rel, ItemPointer otid,
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TupleTableSlot *slot,
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Snapshot snapshot,
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bool *update_indexes)
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{
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TM_Result result;
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TM_FailureData tmfd;
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LockTupleMode lockmode;
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result = table_tuple_update(rel, otid, slot,
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GetCurrentCommandId(true),
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snapshot, InvalidSnapshot,
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true /* wait for commit */ ,
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&tmfd, &lockmode, update_indexes);
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switch (result)
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{
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case TM_SelfModified:
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/* Tuple was already updated in current command? */
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elog(ERROR, "tuple already updated by self");
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break;
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case TM_Ok:
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/* done successfully */
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break;
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case TM_Updated:
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elog(ERROR, "tuple concurrently updated");
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break;
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case TM_Deleted:
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elog(ERROR, "tuple concurrently deleted");
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break;
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default:
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elog(ERROR, "unrecognized table_tuple_update status: %u", result);
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break;
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}
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}
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/* ----------------------------------------------------------------------------
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* Helper functions to implement parallel scans for block oriented AMs.
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* ----------------------------------------------------------------------------
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*/
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Size
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table_block_parallelscan_estimate(Relation rel)
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{
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return sizeof(ParallelBlockTableScanDescData);
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}
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Size
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table_block_parallelscan_initialize(Relation rel, ParallelTableScanDesc pscan)
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{
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ParallelBlockTableScanDesc bpscan = (ParallelBlockTableScanDesc) pscan;
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bpscan->base.phs_relid = RelationGetRelid(rel);
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bpscan->phs_nblocks = RelationGetNumberOfBlocks(rel);
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/* compare phs_syncscan initialization to similar logic in initscan */
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bpscan->base.phs_syncscan = synchronize_seqscans &&
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!RelationUsesLocalBuffers(rel) &&
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bpscan->phs_nblocks > NBuffers / 4;
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SpinLockInit(&bpscan->phs_mutex);
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bpscan->phs_startblock = InvalidBlockNumber;
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pg_atomic_init_u64(&bpscan->phs_nallocated, 0);
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return sizeof(ParallelBlockTableScanDescData);
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}
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void
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table_block_parallelscan_reinitialize(Relation rel, ParallelTableScanDesc pscan)
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{
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ParallelBlockTableScanDesc bpscan = (ParallelBlockTableScanDesc) pscan;
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pg_atomic_write_u64(&bpscan->phs_nallocated, 0);
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}
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/*
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* find and set the scan's startblock
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*
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* Determine where the parallel seq scan should start. This function may be
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* called many times, once by each parallel worker. We must be careful only
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* to set the startblock once.
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*/
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void
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table_block_parallelscan_startblock_init(Relation rel, ParallelBlockTableScanDesc pbscan)
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{
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BlockNumber sync_startpage = InvalidBlockNumber;
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retry:
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/* Grab the spinlock. */
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SpinLockAcquire(&pbscan->phs_mutex);
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/*
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* If the scan's startblock has not yet been initialized, we must do so
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* now. If this is not a synchronized scan, we just start at block 0, but
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* if it is a synchronized scan, we must get the starting position from
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* the synchronized scan machinery. We can't hold the spinlock while
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* doing that, though, so release the spinlock, get the information we
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* need, and retry. If nobody else has initialized the scan in the
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* meantime, we'll fill in the value we fetched on the second time
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* through.
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*/
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if (pbscan->phs_startblock == InvalidBlockNumber)
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{
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if (!pbscan->base.phs_syncscan)
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pbscan->phs_startblock = 0;
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else if (sync_startpage != InvalidBlockNumber)
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pbscan->phs_startblock = sync_startpage;
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else
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{
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SpinLockRelease(&pbscan->phs_mutex);
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sync_startpage = ss_get_location(rel, pbscan->phs_nblocks);
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goto retry;
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}
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}
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SpinLockRelease(&pbscan->phs_mutex);
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}
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/*
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* get the next page to scan
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*
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* Get the next page to scan. Even if there are no pages left to scan,
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* another backend could have grabbed a page to scan and not yet finished
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* looking at it, so it doesn't follow that the scan is done when the first
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* backend gets an InvalidBlockNumber return.
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*/
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BlockNumber
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table_block_parallelscan_nextpage(Relation rel, ParallelBlockTableScanDesc pbscan)
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{
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BlockNumber page;
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uint64 nallocated;
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/*
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* phs_nallocated tracks how many pages have been allocated to workers
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* already. When phs_nallocated >= rs_nblocks, all blocks have been
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* allocated.
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*
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* Because we use an atomic fetch-and-add to fetch the current value, the
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* phs_nallocated counter will exceed rs_nblocks, because workers will
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* still increment the value, when they try to allocate the next block but
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* all blocks have been allocated already. The counter must be 64 bits
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* wide because of that, to avoid wrapping around when rs_nblocks is close
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* to 2^32.
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*
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* The actual page to return is calculated by adding the counter to the
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* starting block number, modulo nblocks.
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*/
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nallocated = pg_atomic_fetch_add_u64(&pbscan->phs_nallocated, 1);
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if (nallocated >= pbscan->phs_nblocks)
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page = InvalidBlockNumber; /* all blocks have been allocated */
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else
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page = (nallocated + pbscan->phs_startblock) % pbscan->phs_nblocks;
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/*
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* Report scan location. Normally, we report the current page number.
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* When we reach the end of the scan, though, we report the starting page,
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* not the ending page, just so the starting positions for later scans
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* doesn't slew backwards. We only report the position at the end of the
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* scan once, though: subsequent callers will report nothing.
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*/
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if (pbscan->base.phs_syncscan)
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{
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if (page != InvalidBlockNumber)
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ss_report_location(rel, page);
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else if (nallocated == pbscan->phs_nblocks)
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ss_report_location(rel, pbscan->phs_startblock);
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}
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return page;
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}
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/* ----------------------------------------------------------------------------
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* Helper functions to implement relation sizing for block oriented AMs.
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* ----------------------------------------------------------------------------
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*/
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/*
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* table_block_relation_size
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*
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* If a table AM uses the various relation forks as the sole place where data
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* is stored, and if it uses them in the expected manner (e.g. the actual data
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* is in the main fork rather than some other), it can use this implementation
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* of the relation_size callback rather than implementing its own.
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*/
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uint64
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table_block_relation_size(Relation rel, ForkNumber forkNumber)
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{
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uint64 nblocks = 0;
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/* Open it at the smgr level if not already done */
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RelationOpenSmgr(rel);
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/* InvalidForkNumber indicates returning the size for all forks */
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if (forkNumber == InvalidForkNumber)
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{
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for (int i = 0; i < MAX_FORKNUM; i++)
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nblocks += smgrnblocks(rel->rd_smgr, i);
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}
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else
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nblocks = smgrnblocks(rel->rd_smgr, forkNumber);
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return nblocks * BLCKSZ;
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}
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/*
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* table_block_relation_estimate_size
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*
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* This function can't be directly used as the implementation of the
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* relation_estimate_size callback, because it has a few additional parameters.
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* Instead, it is intended to be used as a helper function; the caller can
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* pass through the arguments to its relation_estimate_size function plus the
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* additional values required here.
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*
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* overhead_bytes_per_tuple should contain the approximate number of bytes
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* of storage required to store a tuple above and beyond what is required for
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* the tuple data proper. Typically, this would include things like the
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* size of the tuple header and item pointer. This is only used for query
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* planning, so a table AM where the value is not constant could choose to
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* pass a "best guess".
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*
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* usable_bytes_per_page should contain the approximate number of bytes per
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* page usable for tuple data, excluding the page header and any anticipated
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* special space.
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*/
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void
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table_block_relation_estimate_size(Relation rel, int32 *attr_widths,
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BlockNumber *pages, double *tuples,
|
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double *allvisfrac,
|
|
Size overhead_bytes_per_tuple,
|
|
Size usable_bytes_per_page)
|
|
{
|
|
BlockNumber curpages;
|
|
BlockNumber relpages;
|
|
double reltuples;
|
|
BlockNumber relallvisible;
|
|
double density;
|
|
|
|
/* it should have storage, so we can call the smgr */
|
|
curpages = RelationGetNumberOfBlocks(rel);
|
|
|
|
/* coerce values in pg_class to more desirable types */
|
|
relpages = (BlockNumber) rel->rd_rel->relpages;
|
|
reltuples = (double) rel->rd_rel->reltuples;
|
|
relallvisible = (BlockNumber) rel->rd_rel->relallvisible;
|
|
|
|
/*
|
|
* HACK: if the relation has never yet been vacuumed, use a minimum size
|
|
* estimate of 10 pages. The idea here is to avoid assuming a
|
|
* newly-created table is really small, even if it currently is, because
|
|
* that may not be true once some data gets loaded into it. Once a vacuum
|
|
* or analyze cycle has been done on it, it's more reasonable to believe
|
|
* the size is somewhat stable.
|
|
*
|
|
* (Note that this is only an issue if the plan gets cached and used again
|
|
* after the table has been filled. What we're trying to avoid is using a
|
|
* nestloop-type plan on a table that has grown substantially since the
|
|
* plan was made. Normally, autovacuum/autoanalyze will occur once enough
|
|
* inserts have happened and cause cached-plan invalidation; but that
|
|
* doesn't happen instantaneously, and it won't happen at all for cases
|
|
* such as temporary tables.)
|
|
*
|
|
* We approximate "never vacuumed" by "has relpages = 0", which means this
|
|
* will also fire on genuinely empty relations. Not great, but
|
|
* fortunately that's a seldom-seen case in the real world, and it
|
|
* shouldn't degrade the quality of the plan too much anyway to err in
|
|
* this direction.
|
|
*
|
|
* If the table has inheritance children, we don't apply this heuristic.
|
|
* Totally empty parent tables are quite common, so we should be willing
|
|
* to believe that they are empty.
|
|
*/
|
|
if (curpages < 10 &&
|
|
relpages == 0 &&
|
|
!rel->rd_rel->relhassubclass)
|
|
curpages = 10;
|
|
|
|
/* report estimated # pages */
|
|
*pages = curpages;
|
|
/* quick exit if rel is clearly empty */
|
|
if (curpages == 0)
|
|
{
|
|
*tuples = 0;
|
|
*allvisfrac = 0;
|
|
return;
|
|
}
|
|
|
|
/* estimate number of tuples from previous tuple density */
|
|
if (relpages > 0)
|
|
density = reltuples / (double) relpages;
|
|
else
|
|
{
|
|
/*
|
|
* When we have no data because the relation was truncated, estimate
|
|
* tuple width from attribute datatypes. We assume here that the
|
|
* pages are completely full, which is OK for tables (since they've
|
|
* presumably not been VACUUMed yet) but is probably an overestimate
|
|
* for indexes. Fortunately get_relation_info() can clamp the
|
|
* overestimate to the parent table's size.
|
|
*
|
|
* Note: this code intentionally disregards alignment considerations,
|
|
* because (a) that would be gilding the lily considering how crude
|
|
* the estimate is, (b) it creates platform dependencies in the
|
|
* default plans which are kind of a headache for regression testing,
|
|
* and (c) different table AMs might use different padding schemes.
|
|
*/
|
|
int32 tuple_width;
|
|
|
|
tuple_width = get_rel_data_width(rel, attr_widths);
|
|
tuple_width += overhead_bytes_per_tuple;
|
|
/* note: integer division is intentional here */
|
|
density = usable_bytes_per_page / tuple_width;
|
|
}
|
|
*tuples = rint(density * (double) curpages);
|
|
|
|
/*
|
|
* We use relallvisible as-is, rather than scaling it up like we do for
|
|
* the pages and tuples counts, on the theory that any pages added since
|
|
* the last VACUUM are most likely not marked all-visible. But costsize.c
|
|
* wants it converted to a fraction.
|
|
*/
|
|
if (relallvisible == 0 || curpages <= 0)
|
|
*allvisfrac = 0;
|
|
else if ((double) relallvisible >= curpages)
|
|
*allvisfrac = 1;
|
|
else
|
|
*allvisfrac = (double) relallvisible / curpages;
|
|
}
|