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postgres/src/include/access/genam.h
Andres Freund c2fe139c20 tableam: Add and use scan APIs. 
Too allow table accesses to be not directly dependent on heap, several
new abstractions are needed. Specifically:

1) Heap scans need to be generalized into table scans. Do this by
   introducing TableScanDesc, which will be the "base class" for
   individual AMs. This contains the AM independent fields from
   HeapScanDesc.

   The previous heap_{beginscan,rescan,endscan} et al. have been
   replaced with a table_ version.

   There's no direct replacement for heap_getnext(), as that returned
   a HeapTuple, which is undesirable for a other AMs. Instead there's
   table_scan_getnextslot().  But note that heap_getnext() lives on,
   it's still used widely to access catalog tables.

   This is achieved by new scan_begin, scan_end, scan_rescan,
   scan_getnextslot callbacks.

2) The portion of parallel scans that's shared between backends need
   to be able to do so without the user doing per-AM work. To achieve
   that new parallelscan_{estimate, initialize, reinitialize}
   callbacks are introduced, which operate on a new
   ParallelTableScanDesc, which again can be subclassed by AMs.

   As it is likely that several AMs are going to be block oriented,
   block oriented callbacks that can be shared between such AMs are
   provided and used by heap. table_block_parallelscan_{estimate,
   intiialize, reinitialize} as callbacks, and
   table_block_parallelscan_{nextpage, init} for use in AMs. These
   operate on a ParallelBlockTableScanDesc.

3) Index scans need to be able to access tables to return a tuple, and
   there needs to be state across individual accesses to the heap to
   store state like buffers. That's now handled by introducing a
   sort-of-scan IndexFetchTable, which again is intended to be
   subclassed by individual AMs (for heap IndexFetchHeap).

   The relevant callbacks for an AM are index_fetch_{end, begin,
   reset} to create the necessary state, and index_fetch_tuple to
   retrieve an indexed tuple.  Note that index_fetch_tuple
   implementations need to be smarter than just blindly fetching the
   tuples for AMs that have optimizations similar to heap's HOT - the
   currently alive tuple in the update chain needs to be fetched if
   appropriate.

   Similar to table_scan_getnextslot(), it's undesirable to continue
   to return HeapTuples. Thus index_fetch_heap (might want to rename
   that later) now accepts a slot as an argument. Core code doesn't
   have a lot of call sites performing index scans without going
   through the systable_* API (in contrast to loads of heap_getnext
   calls and working directly with HeapTuples).

   Index scans now store the result of a search in
   IndexScanDesc->xs_heaptid, rather than xs_ctup->t_self. As the
   target is not generally a HeapTuple anymore that seems cleaner.

To be able to sensible adapt code to use the above, two further
callbacks have been introduced:

a) slot_callbacks returns a TupleTableSlotOps* suitable for creating
   slots capable of holding a tuple of the AMs
   type. table_slot_callbacks() and table_slot_create() are based
   upon that, but have additional logic to deal with views, foreign
   tables, etc.

   While this change could have been done separately, nearly all the
   call sites that needed to be adapted for the rest of this commit
   also would have been needed to be adapted for
   table_slot_callbacks(), making separation not worthwhile.

b) tuple_satisfies_snapshot checks whether the tuple in a slot is
   currently visible according to a snapshot. That's required as a few
   places now don't have a buffer + HeapTuple around, but a
   slot (which in heap's case internally has that information).

Additionally a few infrastructure changes were needed:

I) SysScanDesc, as used by systable_{beginscan, getnext} et al. now
   internally uses a slot to keep track of tuples. While
   systable_getnext() still returns HeapTuples, and will so for the
   foreseeable future, the index API (see 1) above) now only deals with
   slots.

The remainder, and largest part, of this commit is then adjusting all
scans in postgres to use the new APIs.

Author: Andres Freund, Haribabu Kommi, Alvaro Herrera
Discussion:
    https://postgr.es/m/20180703070645.wchpu5muyto5n647@alap3.anarazel.de
    https://postgr.es/m/20160812231527.GA690404@alvherre.pgsql
2019-03-11 12:46:41 -07:00

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/*-------------------------------------------------------------------------
*
* genam.h
* POSTGRES generalized index access method definitions.
*
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/access/genam.h
*
*-------------------------------------------------------------------------
*/
#ifndef GENAM_H
#define GENAM_H
#include "access/sdir.h"
#include "access/skey.h"
#include "nodes/tidbitmap.h"
#include "storage/lockdefs.h"
#include "utils/relcache.h"
#include "utils/snapshot.h"
/* We don't want this file to depend on execnodes.h. */
struct IndexInfo;
/*
* Struct for statistics returned by ambuild
*/
typedef struct IndexBuildResult
{
double heap_tuples; /* # of tuples seen in parent table */
double index_tuples; /* # of tuples inserted into index */
} IndexBuildResult;
/*
* Struct for input arguments passed to ambulkdelete and amvacuumcleanup
*
* num_heap_tuples is accurate only when estimated_count is false;
* otherwise it's just an estimate (currently, the estimate is the
* prior value of the relation's pg_class.reltuples field). It will
* always just be an estimate during ambulkdelete.
*/
typedef struct IndexVacuumInfo
{
Relation index; /* the index being vacuumed */
bool analyze_only; /* ANALYZE (without any actual vacuum) */
bool estimated_count; /* num_heap_tuples is an estimate */
int message_level; /* ereport level for progress messages */
double num_heap_tuples; /* tuples remaining in heap */
BufferAccessStrategy strategy; /* access strategy for reads */
} IndexVacuumInfo;
/*
* Struct for statistics returned by ambulkdelete and amvacuumcleanup
*
* This struct is normally allocated by the first ambulkdelete call and then
* passed along through subsequent ones until amvacuumcleanup; however,
* amvacuumcleanup must be prepared to allocate it in the case where no
* ambulkdelete calls were made (because no tuples needed deletion).
* Note that an index AM could choose to return a larger struct
* of which this is just the first field; this provides a way for ambulkdelete
* to communicate additional private data to amvacuumcleanup.
*
* Note: pages_removed is the amount by which the index physically shrank,
* if any (ie the change in its total size on disk). pages_deleted and
* pages_free refer to free space within the index file. Some index AMs
* may compute num_index_tuples by reference to num_heap_tuples, in which
* case they should copy the estimated_count field from IndexVacuumInfo.
*/
typedef struct IndexBulkDeleteResult
{
BlockNumber num_pages; /* pages remaining in index */
BlockNumber pages_removed; /* # removed during vacuum operation */
bool estimated_count; /* num_index_tuples is an estimate */
double num_index_tuples; /* tuples remaining */
double tuples_removed; /* # removed during vacuum operation */
BlockNumber pages_deleted; /* # unused pages in index */
BlockNumber pages_free; /* # pages available for reuse */
} IndexBulkDeleteResult;
/* Typedef for callback function to determine if a tuple is bulk-deletable */
typedef bool (*IndexBulkDeleteCallback) (ItemPointer itemptr, void *state);
/* struct definitions appear in relscan.h */
typedef struct IndexScanDescData *IndexScanDesc;
typedef struct SysScanDescData *SysScanDesc;
typedef struct ParallelIndexScanDescData *ParallelIndexScanDesc;
/*
* Enumeration specifying the type of uniqueness check to perform in
* index_insert().
*
* UNIQUE_CHECK_YES is the traditional Postgres immediate check, possibly
* blocking to see if a conflicting transaction commits.
*
* For deferrable unique constraints, UNIQUE_CHECK_PARTIAL is specified at
* insertion time. The index AM should test if the tuple is unique, but
* should not throw error, block, or prevent the insertion if the tuple
* appears not to be unique. We'll recheck later when it is time for the
* constraint to be enforced. The AM must return true if the tuple is
* known unique, false if it is possibly non-unique. In the "true" case
* it is safe to omit the later recheck.
*
* When it is time to recheck the deferred constraint, a pseudo-insertion
* call is made with UNIQUE_CHECK_EXISTING. The tuple is already in the
* index in this case, so it should not be inserted again. Rather, just
* check for conflicting live tuples (possibly blocking).
*/
typedef enum IndexUniqueCheck
{
UNIQUE_CHECK_NO, /* Don't do any uniqueness checking */
UNIQUE_CHECK_YES, /* Enforce uniqueness at insertion time */
UNIQUE_CHECK_PARTIAL, /* Test uniqueness, but no error */
UNIQUE_CHECK_EXISTING /* Check if existing tuple is unique */
} IndexUniqueCheck;
/*
* generalized index_ interface routines (in indexam.c)
*/
/*
* IndexScanIsValid
* True iff the index scan is valid.
*/
#define IndexScanIsValid(scan) PointerIsValid(scan)
extern Relation index_open(Oid relationId, LOCKMODE lockmode);
extern void index_close(Relation relation, LOCKMODE lockmode);
extern bool index_insert(Relation indexRelation,
Datum *values, bool *isnull,
ItemPointer heap_t_ctid,
Relation heapRelation,
IndexUniqueCheck checkUnique,
struct IndexInfo *indexInfo);
extern IndexScanDesc index_beginscan(Relation heapRelation,
Relation indexRelation,
Snapshot snapshot,
int nkeys, int norderbys);
extern IndexScanDesc index_beginscan_bitmap(Relation indexRelation,
Snapshot snapshot,
int nkeys);
extern void index_rescan(IndexScanDesc scan,
ScanKey keys, int nkeys,
ScanKey orderbys, int norderbys);
extern void index_endscan(IndexScanDesc scan);
extern void index_markpos(IndexScanDesc scan);
extern void index_restrpos(IndexScanDesc scan);
extern Size index_parallelscan_estimate(Relation indexrel, Snapshot snapshot);
extern void index_parallelscan_initialize(Relation heaprel, Relation indexrel,
Snapshot snapshot, ParallelIndexScanDesc target);
extern void index_parallelrescan(IndexScanDesc scan);
extern IndexScanDesc index_beginscan_parallel(Relation heaprel,
Relation indexrel, int nkeys, int norderbys,
ParallelIndexScanDesc pscan);
extern ItemPointer index_getnext_tid(IndexScanDesc scan,
ScanDirection direction);
struct TupleTableSlot;
extern bool index_fetch_heap(IndexScanDesc scan, struct TupleTableSlot *slot);
extern bool index_getnext_slot(IndexScanDesc scan, ScanDirection direction,
struct TupleTableSlot *slot);
extern int64 index_getbitmap(IndexScanDesc scan, TIDBitmap *bitmap);
extern IndexBulkDeleteResult *index_bulk_delete(IndexVacuumInfo *info,
IndexBulkDeleteResult *stats,
IndexBulkDeleteCallback callback,
void *callback_state);
extern IndexBulkDeleteResult *index_vacuum_cleanup(IndexVacuumInfo *info,
IndexBulkDeleteResult *stats);
extern bool index_can_return(Relation indexRelation, int attno);
extern RegProcedure index_getprocid(Relation irel, AttrNumber attnum,
uint16 procnum);
extern FmgrInfo *index_getprocinfo(Relation irel, AttrNumber attnum,
uint16 procnum);
extern void index_store_float8_orderby_distances(IndexScanDesc scan,
Oid *orderByTypes, double *distances,
bool recheckOrderBy);
/*
* index access method support routines (in genam.c)
*/
extern IndexScanDesc RelationGetIndexScan(Relation indexRelation,
int nkeys, int norderbys);
extern void IndexScanEnd(IndexScanDesc scan);
extern char *BuildIndexValueDescription(Relation indexRelation,
Datum *values, bool *isnull);
/*
* heap-or-index access to system catalogs (in genam.c)
*/
extern SysScanDesc systable_beginscan(Relation heapRelation,
Oid indexId,
bool indexOK,
Snapshot snapshot,
int nkeys, ScanKey key);
extern HeapTuple systable_getnext(SysScanDesc sysscan);
extern bool systable_recheck_tuple(SysScanDesc sysscan, HeapTuple tup);
extern void systable_endscan(SysScanDesc sysscan);
extern SysScanDesc systable_beginscan_ordered(Relation heapRelation,
Relation indexRelation,
Snapshot snapshot,
int nkeys, ScanKey key);
extern HeapTuple systable_getnext_ordered(SysScanDesc sysscan,
ScanDirection direction);
extern void systable_endscan_ordered(SysScanDesc sysscan);
#endif /* GENAM_H */
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