indexam.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

 * NOTE: this only restores the internal scan state of the index AM.
 * The current result tuple (scan->xs_ctup) doesn't change.  See comments
 * for ExecRestrPos().
 * ----------------
 */
void
index_restrpos(IndexScanDesc scan)
{
	FmgrInfo   *procedure;

	SCAN_CHECKS;
	GET_SCAN_PROCEDURE(amrestrpos);

	scan->kill_prior_tuple = false;		/* for safety */

	/*
	 * We do not reset got_tuple; so if the scan is actually being
	 * short-circuited by index_getnext, the effective position restoration is
	 * done by restoring unique_tuple_pos.
	 */
	scan->unique_tuple_pos = scan->unique_tuple_mark;

	FunctionCall1(procedure, PointerGetDatum(scan));
}

/* ----------------
 *		index_getnext - get the next heap tuple from a scan
 *
 * The result is the next heap tuple satisfying the scan keys and the
 * snapshot, or NULL if no more matching tuples exist.	On success,
 * the buffer containing the heap tuple is pinned (the pin will be dropped
 * at the next index_getnext or index_endscan).  The index TID corresponding
 * to the heap tuple can be obtained if needed from scan->currentItemData.
 * ----------------
 */
HeapTuple
index_getnext(IndexScanDesc scan, ScanDirection direction)
{
	HeapTuple	heapTuple = &scan->xs_ctup;
	FmgrInfo   *procedure;

	SCAN_CHECKS;
	GET_SCAN_PROCEDURE(amgettuple);

	/*
	 * If we already got a tuple and it must be unique, there's no need to
	 * make the index AM look through any additional tuples.  (This can save a
	 * useful amount of work in scenarios where there are many dead tuples due
	 * to heavy update activity.)
	 *
	 * To do this we must keep track of the logical scan position
	 * (before/on/after tuple).  Also, we have to be sure to release scan
	 * resources before returning NULL; if we fail to do so then a multi-index
	 * scan can easily run the system out of free buffers.	We can release
	 * index-level resources fairly cheaply by calling index_rescan.  This
	 * means there are two persistent states as far as the index AM is
	 * concerned: on-tuple and rescanned.  If we are actually asked to
	 * re-fetch the single tuple, we have to go through a fresh indexscan
	 * startup, which penalizes that (infrequent) case.
	 */
	if (scan->keys_are_unique && scan->got_tuple)
	{
		int			new_tuple_pos = scan->unique_tuple_pos;

		if (ScanDirectionIsForward(direction))
		{
			if (new_tuple_pos <= 0)
				new_tuple_pos++;
		}
		else
		{
			if (new_tuple_pos >= 0)
				new_tuple_pos--;
		}
		if (new_tuple_pos == 0)
		{
			/*
			 * We are moving onto the unique tuple from having been off it. We
			 * just fall through and let the index AM do the work. Note we
			 * should get the right answer regardless of scan direction.
			 */
			scan->unique_tuple_pos = 0; /* need to update position */
		}
		else
		{
			/*
			 * Moving off the tuple; must do amrescan to release index-level
			 * pins before we return NULL.	Since index_rescan will reset my
			 * state, must save and restore...
			 */
			int			unique_tuple_mark = scan->unique_tuple_mark;

			index_rescan(scan, NULL /* no change to key */ );

			scan->keys_are_unique = true;
			scan->got_tuple = true;
			scan->unique_tuple_pos = new_tuple_pos;
			scan->unique_tuple_mark = unique_tuple_mark;

			return NULL;
		}
	}

	/* just make sure this is false... */
	scan->kill_prior_tuple = false;

	for (;;)
	{
		bool		found;

		/*
		 * The AM's gettuple proc finds the next tuple matching the scan keys.
		 */
		found = DatumGetBool(FunctionCall2(procedure,
										   PointerGetDatum(scan),
										   Int32GetDatum(direction)));

		/* Reset kill flag immediately for safety */
		scan->kill_prior_tuple = false;

		if (!found)
		{
			/* Release any held pin on a heap page */
			if (BufferIsValid(scan->xs_cbuf))
			{
				ReleaseBuffer(scan->xs_cbuf);
				scan->xs_cbuf = InvalidBuffer;
			}
			return NULL;		/* failure exit */
		}

		pgstat_count_index_tuples(&scan->xs_pgstat_info, 1);

		/*
		 * Fetch the heap tuple and see if it matches the snapshot.
		 */
		if (heap_release_fetch(scan->heapRelation, scan->xs_snapshot,
							   heapTuple, &scan->xs_cbuf, true,
							   &scan->xs_pgstat_info))
			break;

		/* Skip if no undeleted tuple at this location */
		if (heapTuple->t_data == NULL)
			continue;

		/*
		 * If we can't see it, maybe no one else can either.  Check to see if
		 * the tuple is dead to all transactions.  If so, signal the index AM
		 * to not return it on future indexscans.
		 *
		 * We told heap_release_fetch to keep a pin on the buffer, so we can
		 * re-access the tuple here.  But we must re-lock the buffer first.
		 */
		LockBuffer(scan->xs_cbuf, BUFFER_LOCK_SHARE);

		if (HeapTupleSatisfiesVacuum(heapTuple->t_data, RecentGlobalXmin,
									 scan->xs_cbuf) == HEAPTUPLE_DEAD)
			scan->kill_prior_tuple = true;

		LockBuffer(scan->xs_cbuf, BUFFER_LOCK_UNLOCK);
	}

	/* Success exit */
	scan->got_tuple = true;

	/*
	 * If we just fetched a known-unique tuple, then subsequent calls will go
	 * through the short-circuit code above.  unique_tuple_pos has been
	 * initialized to 0, which is the correct state ("on row").
	 */

	return heapTuple;
}

/* ----------------
 *		index_getnext_indexitem - get the next index tuple from a scan
 *
 * Finds the next index tuple satisfying the scan keys.  Note that the
 * corresponding heap tuple is not accessed, and thus no time qual (snapshot)
 * check is done, other than the index AM's internal check for killed tuples
 * (which most callers of this routine will probably want to suppress by
 * setting scan->ignore_killed_tuples = false).
 *
 * On success (TRUE return), the found index TID is in scan->currentItemData,
 * and its heap TID is in scan->xs_ctup.t_self.  scan->xs_cbuf is untouched.
 * ----------------
 */
bool
index_getnext_indexitem(IndexScanDesc scan,
						ScanDirection direction)
{
	FmgrInfo   *procedure;
	bool		found;

	SCAN_CHECKS;
	GET_SCAN_PROCEDURE(amgettuple);

	/* just make sure this is false... */
	scan->kill_prior_tuple = false;

	/*
	 * have the am's gettuple proc do all the work.
	 */
	found = DatumGetBool(FunctionCall2(procedure,
									   PointerGetDatum(scan),
									   Int32GetDatum(direction)));

	if (found)
		pgstat_count_index_tuples(&scan->xs_pgstat_info, 1);

	return found;
}

/* ----------------
 *		index_getmulti - get multiple tuples from an index scan
 *
 * Collects the TIDs of multiple heap tuples satisfying the scan keys.
 * Since there's no interlock between the index scan and the eventual heap
 * access, this is only safe to use with MVCC-based snapshots: the heap
 * item slot could have been replaced by a newer tuple by the time we get
 * to it.
 *
 * A TRUE result indicates more calls should occur; a FALSE result says the
 * scan is done.  *returned_tids could be zero or nonzero in either case.
 * ----------------
 */
bool
index_getmulti(IndexScanDesc scan,
			   ItemPointer tids, int32 max_tids,
			   int32 *returned_tids)
{
	FmgrInfo   *procedure;
	bool		found;

	SCAN_CHECKS;
	GET_SCAN_PROCEDURE(amgetmulti);

	/* just make sure this is false... */
	scan->kill_prior_tuple = false;

	/*
	 * have the am's getmulti proc do all the work.
	 */
	found = DatumGetBool(FunctionCall4(procedure,
									   PointerGetDatum(scan),
									   PointerGetDatum(tids),
									   Int32GetDatum(max_tids),
									   PointerGetDatum(returned_tids)));

	pgstat_count_index_tuples(&scan->xs_pgstat_info, *returned_tids);

	return found;
}

/* ----------------
 *		index_bulk_delete - do mass deletion of index entries
 *
 *		callback routine tells whether a given main-heap tuple is
 *		to be deleted
 *
 *		return value is an optional palloc'd struct of statistics
 * ----------------
 */
IndexBulkDeleteResult *
index_bulk_delete(Relation indexRelation,
				  IndexBulkDeleteCallback callback,
				  void *callback_state)
{
	FmgrInfo   *procedure;
	IndexBulkDeleteResult *result;

	RELATION_CHECKS;
	GET_REL_PROCEDURE(ambulkdelete);

	result = (IndexBulkDeleteResult *)
		DatumGetPointer(FunctionCall3(procedure,
									  PointerGetDatum(indexRelation),
									  PointerGetDatum((Pointer) callback),
									  PointerGetDatum(callback_state)));

	return result;
}

/* ----------------
 *		index_vacuum_cleanup - do post-deletion cleanup of an index
 *
 *		return value is an optional palloc'd struct of statistics
 * ----------------
 */
IndexBulkDeleteResult *
index_vacuum_cleanup(Relation indexRelation,
					 IndexVacuumCleanupInfo *info,
					 IndexBulkDeleteResult *stats)
{
	FmgrInfo   *procedure;
	IndexBulkDeleteResult *result;

	RELATION_CHECKS;

	/* It's okay for an index AM not to have a vacuumcleanup procedure */
	if (!RegProcedureIsValid(indexRelation->rd_am->amvacuumcleanup))
		return stats;

	GET_REL_PROCEDURE(amvacuumcleanup);

	result = (IndexBulkDeleteResult *)
		DatumGetPointer(FunctionCall3(procedure,
									  PointerGetDatum(indexRelation),
									  PointerGetDatum((Pointer) info),
									  PointerGetDatum((Pointer) stats)));

	return result;
}

/* ----------------
 *		index_getprocid
 *
 *		Some indexed access methods may require support routines that are
 *		not in the operator class/operator model imposed by pg_am.	These
 *		access methods may store the OIDs of registered procedures they
 *		need in pg_amproc.	These registered procedure OIDs are ordered in
 *		a way that makes sense to the access method, and used only by the
 *		access method.	The general index code doesn't know anything about
 *		the routines involved; it just builds an ordered list of them for
 *		each attribute on which an index is defined.
 *
 *		This routine returns the requested procedure OID for a particular
 *		indexed attribute.
 * ----------------
 */
RegProcedure
index_getprocid(Relation irel,
				AttrNumber attnum,
				uint16 procnum)
{
	RegProcedure *loc;
	int			nproc;
	int			procindex;

	nproc = irel->rd_am->amsupport;

	Assert(procnum > 0 && procnum <= (uint16) nproc);

	procindex = (nproc * (attnum - 1)) + (procnum - 1);

	loc = irel->rd_support;

	Assert(loc != NULL);

	return loc[procindex];
}

/* ----------------
 *		index_getprocinfo
 *
 *		This routine allows index AMs to keep fmgr lookup info for
 *		support procs in the relcache.
 *
 * Note: the return value points into cached data that will be lost during
 * any relcache rebuild!  Therefore, either use the callinfo right away,
 * or save it only after having acquired some type of lock on the index rel.
 * ----------------
 */
FmgrInfo *
index_getprocinfo(Relation irel,
				  AttrNumber attnum,
				  uint16 procnum)
{
	FmgrInfo   *locinfo;
	int			nproc;
	int			procindex;

	nproc = irel->rd_am->amsupport;

	Assert(procnum > 0 && procnum <= (uint16) nproc);

	procindex = (nproc * (attnum - 1)) + (procnum - 1);

	locinfo = irel->rd_supportinfo;

	Assert(locinfo != NULL);

	locinfo += procindex;

	/* Initialize the lookup info if first time through */
	if (locinfo->fn_oid == InvalidOid)
	{
		RegProcedure *loc = irel->rd_support;
		RegProcedure procId;

		Assert(loc != NULL);

		procId = loc[procindex];

		/*
		 * Complain if function was not found during IndexSupportInitialize.
		 * This should not happen unless the system tables contain bogus
		 * entries for the index opclass.  (If an AM wants to allow a support
		 * function to be optional, it can use index_getprocid.)
		 */
		if (!RegProcedureIsValid(procId))
			elog(ERROR, "missing support function %d for attribute %d of index \"%s\"",
				 procnum, attnum, RelationGetRelationName(irel));

		fmgr_info_cxt(procId, locinfo, irel->rd_indexcxt);
	}

	return locinfo;
}