indexam.c

postgresql8.3.4源码,开源数据库

			 */
			Assert(BufferIsValid(scan->xs_cbuf));
			Assert(ItemPointerGetBlockNumber(tid) ==
				   BufferGetBlockNumber(scan->xs_cbuf));
			Assert(TransactionIdIsValid(scan->xs_prev_xmax));
			offnum = scan->xs_next_hot;
			at_chain_start = false;
			scan->xs_next_hot = InvalidOffsetNumber;
		}
		else
		{
			bool		found;
			Buffer		prev_buf;

			/*
			 * If we scanned a whole HOT chain and found only dead tuples,
			 * tell index AM to kill its entry for that TID.
			 */
			scan->kill_prior_tuple = scan->xs_hot_dead;

			/*
			 * The AM's gettuple proc finds the next index entry matching the
			 * scan keys, and puts the TID in xs_ctup.t_self (ie, *tid).
			 */
			found = DatumGetBool(FunctionCall2(procedure,
											   PointerGetDatum(scan),
											   Int32GetDatum(direction)));

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

			/* If we're out of index entries, break out of outer loop */
			if (!found)
				break;

			pgstat_count_index_tuples(scan->indexRelation, 1);

			/* Switch to correct buffer if we don't have it already */
			prev_buf = scan->xs_cbuf;
			scan->xs_cbuf = ReleaseAndReadBuffer(scan->xs_cbuf,
												 scan->heapRelation,
											 ItemPointerGetBlockNumber(tid));

			/*
			 * Prune page, but only if we weren't already on this page
			 */
			if (prev_buf != scan->xs_cbuf)
				heap_page_prune_opt(scan->heapRelation, scan->xs_cbuf,
									RecentGlobalXmin);

			/* Prepare to scan HOT chain starting at index-referenced offnum */
			offnum = ItemPointerGetOffsetNumber(tid);
			at_chain_start = true;

			/* We don't know what the first tuple's xmin should be */
			scan->xs_prev_xmax = InvalidTransactionId;

			/* Initialize flag to detect if all entries are dead */
			scan->xs_hot_dead = true;
		}

		/* Obtain share-lock on the buffer so we can examine visibility */
		LockBuffer(scan->xs_cbuf, BUFFER_LOCK_SHARE);

		dp = (Page) BufferGetPage(scan->xs_cbuf);

		/* Scan through possible multiple members of HOT-chain */
		for (;;)
		{
			ItemId		lp;
			ItemPointer ctid;

			/* check for bogus TID */
			if (offnum < FirstOffsetNumber ||
				offnum > PageGetMaxOffsetNumber(dp))
				break;

			lp = PageGetItemId(dp, offnum);

			/* check for unused, dead, or redirected items */
			if (!ItemIdIsNormal(lp))
			{
				/* We should only see a redirect at start of chain */
				if (ItemIdIsRedirected(lp) && at_chain_start)
				{
					/* Follow the redirect */
					offnum = ItemIdGetRedirect(lp);
					at_chain_start = false;
					continue;
				}
				/* else must be end of chain */
				break;
			}

			/*
			 * We must initialize all of *heapTuple (ie, scan->xs_ctup) since
			 * it is returned to the executor on success.
			 */
			heapTuple->t_data = (HeapTupleHeader) PageGetItem(dp, lp);
			heapTuple->t_len = ItemIdGetLength(lp);
			ItemPointerSetOffsetNumber(tid, offnum);
			heapTuple->t_tableOid = RelationGetRelid(scan->heapRelation);
			ctid = &heapTuple->t_data->t_ctid;

			/*
			 * Shouldn't see a HEAP_ONLY tuple at chain start.  (This test
			 * should be unnecessary, since the chain root can't be removed
			 * while we have pin on the index entry, but let's make it
			 * anyway.)
			 */
			if (at_chain_start && HeapTupleIsHeapOnly(heapTuple))
				break;

			/*
			 * The xmin should match the previous xmax value, else chain is
			 * broken.	(Note: this test is not optional because it protects
			 * us against the case where the prior chain member's xmax aborted
			 * since we looked at it.)
			 */
			if (TransactionIdIsValid(scan->xs_prev_xmax) &&
				!TransactionIdEquals(scan->xs_prev_xmax,
								  HeapTupleHeaderGetXmin(heapTuple->t_data)))
				break;

			/* If it's visible per the snapshot, we must return it */
			if (HeapTupleSatisfiesVisibility(heapTuple, scan->xs_snapshot,
											 scan->xs_cbuf))
			{
				/*
				 * If the snapshot is MVCC, we know that it could accept at
				 * most one member of the HOT chain, so we can skip examining
				 * any more members.  Otherwise, check for continuation of the
				 * HOT-chain, and set state for next time.
				 */
				if (IsMVCCSnapshot(scan->xs_snapshot))
					scan->xs_next_hot = InvalidOffsetNumber;
				else if (HeapTupleIsHotUpdated(heapTuple))
				{
					Assert(ItemPointerGetBlockNumber(ctid) ==
						   ItemPointerGetBlockNumber(tid));
					scan->xs_next_hot = ItemPointerGetOffsetNumber(ctid);
					scan->xs_prev_xmax = HeapTupleHeaderGetXmax(heapTuple->t_data);
				}
				else
					scan->xs_next_hot = InvalidOffsetNumber;

				LockBuffer(scan->xs_cbuf, BUFFER_LOCK_UNLOCK);

				pgstat_count_heap_fetch(scan->indexRelation);

				return heapTuple;
			}

			/*
			 * If we can't see it, maybe no one else can either.  Check to see
			 * if the tuple is dead to all transactions.  If we find that all
			 * the tuples in the HOT chain are dead, we'll signal the index AM
			 * to not return that TID on future indexscans.
			 */
			if (scan->xs_hot_dead &&
				HeapTupleSatisfiesVacuum(heapTuple->t_data, RecentGlobalXmin,
										 scan->xs_cbuf) != HEAPTUPLE_DEAD)
				scan->xs_hot_dead = false;

			/*
			 * Check to see if HOT chain continues past this tuple; if so
			 * fetch the next offnum (we don't bother storing it into
			 * xs_next_hot, but must store xs_prev_xmax), and loop around.
			 */
			if (HeapTupleIsHotUpdated(heapTuple))
			{
				Assert(ItemPointerGetBlockNumber(ctid) ==
					   ItemPointerGetBlockNumber(tid));
				offnum = ItemPointerGetOffsetNumber(ctid);
				at_chain_start = false;
				scan->xs_prev_xmax = HeapTupleHeaderGetXmax(heapTuple->t_data);
			}
			else
				break;			/* end of chain */
		}						/* loop over a single HOT chain */

		LockBuffer(scan->xs_cbuf, BUFFER_LOCK_UNLOCK);

		/* Loop around to ask index AM for another TID */
		scan->xs_next_hot = InvalidOffsetNumber;
	}

	/* 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 */
}

/* ----------------
 *		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 heap TID of the found index entry 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->indexRelation, 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->indexRelation, *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(IndexVacuumInfo *info,
				  IndexBulkDeleteResult *stats,
				  IndexBulkDeleteCallback callback,
				  void *callback_state)
{
	Relation	indexRelation = info->index;
	FmgrInfo   *procedure;
	IndexBulkDeleteResult *result;

	RELATION_CHECKS;
	GET_REL_PROCEDURE(ambulkdelete);

	result = (IndexBulkDeleteResult *)
		DatumGetPointer(FunctionCall4(procedure,
									  PointerGetDatum(info),
									  PointerGetDatum(stats),
									  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(IndexVacuumInfo *info,
					 IndexBulkDeleteResult *stats)
{
	Relation	indexRelation = info->index;
	FmgrInfo   *procedure;
	IndexBulkDeleteResult *result;

	RELATION_CHECKS;
	GET_REL_PROCEDURE(amvacuumcleanup);

	result = (IndexBulkDeleteResult *)
		DatumGetPointer(FunctionCall2(procedure,
									  PointerGetDatum(info),
									  PointerGetDatum(stats)));

	return result;
}

/* ----------------
 *		index_getprocid
 *
 *		Index access methods typically require support routines that are
 *		not directly the implementation of any WHERE-clause query operator
 *		and so cannot be kept in pg_amop.  Instead, such routines are kept
 *		in pg_amproc.  These registered procedure OIDs are assigned numbers
 *		according to a convention established 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.
 *
 *		As of Postgres 8.3, support routines within an operator family
 *		are further subdivided by the "left type" and "right type" of the
 *		query operator(s) that they support.  The "default" functions for a
 *		particular indexed attribute are those with both types equal to
 *		the index opclass' opcintype (note that this is subtly different
 *		from the indexed attribute's own type: it may be a binary-compatible
 *		type instead).	Only the default functions are stored in relcache
 *		entries --- access methods can use the syscache to look up non-default
 *		functions.
 *
 *		This routine returns the requested default 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.	As above, only the "default"
 *		functions for any particular indexed attribute are cached.
 *
 * 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;
}