pruneheap.c

postgresql8.3.4源码,开源数据库

			continue;
		}

		/*
		 * Likewise, a dead item pointer can't be part of the chain. (We
		 * already eliminated the case of dead root tuple outside this
		 * function.)
		 */
		if (ItemIdIsDead(lp))
			break;

		Assert(ItemIdIsNormal(lp));
		htup = (HeapTupleHeader) PageGetItem(dp, lp);

		/*
		 * Check the tuple XMIN against prior XMAX, if any
		 */
		if (TransactionIdIsValid(priorXmax) &&
			!TransactionIdEquals(HeapTupleHeaderGetXmin(htup), priorXmax))
			break;

		/*
		 * OK, this tuple is indeed a member of the chain.
		 */
		chainitems[nchain++] = offnum;

		/*
		 * Check tuple's visibility status.
		 */
		tupdead = recent_dead = false;

		switch (HeapTupleSatisfiesVacuum(htup, OldestXmin, buffer))
		{
			case HEAPTUPLE_DEAD:
				tupdead = true;
				break;

			case HEAPTUPLE_RECENTLY_DEAD:
				recent_dead = true;

				/*
				 * This tuple may soon become DEAD.  Update the hint field so
				 * that the page is reconsidered for pruning in future.
				 */
				heap_prune_record_prunable(prstate,
										   HeapTupleHeaderGetXmax(htup));
				break;

			case HEAPTUPLE_DELETE_IN_PROGRESS:

				/*
				 * This tuple may soon become DEAD.  Update the hint field so
				 * that the page is reconsidered for pruning in future.
				 */
				heap_prune_record_prunable(prstate,
										   HeapTupleHeaderGetXmax(htup));
				break;

			case HEAPTUPLE_LIVE:
			case HEAPTUPLE_INSERT_IN_PROGRESS:

				/*
				 * If we wanted to optimize for aborts, we might consider
				 * marking the page prunable when we see INSERT_IN_PROGRESS.
				 * But we don't.  See related decisions about when to mark the
				 * page prunable in heapam.c.
				 */
				break;

			default:
				elog(ERROR, "unexpected HeapTupleSatisfiesVacuum result");
				break;
		}

		/*
		 * Remember the last DEAD tuple seen.  We will advance past
		 * RECENTLY_DEAD tuples just in case there's a DEAD one after them;
		 * but we can't advance past anything else.  (XXX is it really worth
		 * continuing to scan beyond RECENTLY_DEAD?  The case where we will
		 * find another DEAD tuple is a fairly unusual corner case.)
		 */
		if (tupdead)
			latestdead = offnum;
		else if (!recent_dead)
			break;

		/*
		 * If the tuple is not HOT-updated, then we are at the end of this
		 * HOT-update chain.
		 */
		if (!HeapTupleHeaderIsHotUpdated(htup))
			break;

		/*
		 * Advance to next chain member.
		 */
		Assert(ItemPointerGetBlockNumber(&htup->t_ctid) ==
			   BufferGetBlockNumber(buffer));
		offnum = ItemPointerGetOffsetNumber(&htup->t_ctid);
		priorXmax = HeapTupleHeaderGetXmax(htup);
	}

	/*
	 * If we found a DEAD tuple in the chain, adjust the HOT chain so that all
	 * the DEAD tuples at the start of the chain are removed and the root line
	 * pointer is appropriately redirected.
	 */
	if (OffsetNumberIsValid(latestdead))
	{
		/*
		 * Mark as unused each intermediate item that we are able to remove
		 * from the chain.
		 *
		 * When the previous item is the last dead tuple seen, we are at the
		 * right candidate for redirection.
		 */
		for (i = 1; (i < nchain) && (chainitems[i - 1] != latestdead); i++)
		{
			heap_prune_record_unused(prstate, chainitems[i]);
			ndeleted++;
		}

		/*
		 * If the root entry had been a normal tuple, we are deleting it, so
		 * count it in the result.	But changing a redirect (even to DEAD
		 * state) doesn't count.
		 */
		if (ItemIdIsNormal(rootlp))
			ndeleted++;

		/*
		 * If the DEAD tuple is at the end of the chain, the entire chain is
		 * dead and the root line pointer can be marked dead.  Otherwise just
		 * redirect the root to the correct chain member.
		 */
		if (i >= nchain)
			heap_prune_record_dead(prstate, rootoffnum);
		else
		{
			heap_prune_record_redirect(prstate, rootoffnum, chainitems[i]);
			/* If the redirection will be a move, need more processing */
			if (redirect_move)
				redirect_target = chainitems[i];
		}
	}
	else if (nchain < 2 && ItemIdIsRedirected(rootlp))
	{
		/*
		 * We found a redirect item that doesn't point to a valid follow-on
		 * item.  This can happen if the loop in heap_page_prune caused us to
		 * visit the dead successor of a redirect item before visiting the
		 * redirect item.  We can clean up by setting the redirect item to
		 * DEAD state.
		 */
		heap_prune_record_dead(prstate, rootoffnum);
	}
	else if (redirect_move && ItemIdIsRedirected(rootlp))
	{
		/*
		 * If we desire to eliminate LP_REDIRECT items by moving tuples,
		 * make a redirection entry for each redirected root item; this
		 * will cause heap_page_prune_execute to actually do the move.
		 * (We get here only when there are no DEAD tuples in the chain;
		 * otherwise the redirection entry was made above.)
		 */
		heap_prune_record_redirect(prstate, rootoffnum, chainitems[1]);
		redirect_target = chainitems[1];
	}

	/*
	 * If we are going to implement a redirect by moving tuples, we have
	 * to issue a cache invalidation against the redirection target tuple,
	 * because its CTID will be effectively changed by the move.  Note that
	 * CacheInvalidateHeapTuple only queues the request, it doesn't send it;
	 * if we fail before reaching EndNonTransactionalInvalidation, nothing
	 * happens and no harm is done.
	 */
	if (OffsetNumberIsValid(redirect_target))
	{
		ItemId		firstlp = PageGetItemId(dp, redirect_target);
		HeapTupleData firsttup;

		Assert(ItemIdIsNormal(firstlp));
		/* Set up firsttup to reference the tuple at its existing CTID */
		firsttup.t_data = (HeapTupleHeader) PageGetItem(dp, firstlp);
		firsttup.t_len = ItemIdGetLength(firstlp);
		ItemPointerSet(&firsttup.t_self,
					   BufferGetBlockNumber(buffer),
					   redirect_target);
		firsttup.t_tableOid = RelationGetRelid(relation);
		CacheInvalidateHeapTuple(relation, &firsttup);
	}

	return ndeleted;
}

/* Record lowest soon-prunable XID */
static void
heap_prune_record_prunable(PruneState *prstate, TransactionId xid)
{
	/*
	 * This should exactly match the PageSetPrunable macro.  We can't store
	 * directly into the page header yet, so we update working state.
	 */
	Assert(TransactionIdIsNormal(xid));
	if (!TransactionIdIsValid(prstate->new_prune_xid) ||
		TransactionIdPrecedes(xid, prstate->new_prune_xid))
		prstate->new_prune_xid = xid;
}

/* Record item pointer to be redirected */
static void
heap_prune_record_redirect(PruneState *prstate,
						   OffsetNumber offnum, OffsetNumber rdoffnum)
{
	Assert(prstate->nredirected < MaxHeapTuplesPerPage);
	prstate->redirected[prstate->nredirected * 2] = offnum;
	prstate->redirected[prstate->nredirected * 2 + 1] = rdoffnum;
	prstate->nredirected++;
	Assert(!prstate->marked[offnum]);
	prstate->marked[offnum] = true;
	Assert(!prstate->marked[rdoffnum]);
	prstate->marked[rdoffnum] = true;
}

/* Record item pointer to be marked dead */
static void
heap_prune_record_dead(PruneState *prstate, OffsetNumber offnum)
{
	Assert(prstate->ndead < MaxHeapTuplesPerPage);
	prstate->nowdead[prstate->ndead] = offnum;
	prstate->ndead++;
	Assert(!prstate->marked[offnum]);
	prstate->marked[offnum] = true;
}

/* Record item pointer to be marked unused */
static void
heap_prune_record_unused(PruneState *prstate, OffsetNumber offnum)
{
	Assert(prstate->nunused < MaxHeapTuplesPerPage);
	prstate->nowunused[prstate->nunused] = offnum;
	prstate->nunused++;
	Assert(!prstate->marked[offnum]);
	prstate->marked[offnum] = true;
}


/*
 * Perform the actual page changes needed by heap_page_prune.
 * It is expected that the caller has suitable pin and lock on the
 * buffer, and is inside a critical section.
 *
 * This is split out because it is also used by heap_xlog_clean()
 * to replay the WAL record when needed after a crash.  Note that the
 * arguments are identical to those of log_heap_clean().
 */
void
heap_page_prune_execute(Relation reln, Buffer buffer,
						OffsetNumber *redirected, int nredirected,
						OffsetNumber *nowdead, int ndead,
						OffsetNumber *nowunused, int nunused,
						bool redirect_move)
{
	Page		page = (Page) BufferGetPage(buffer);
	OffsetNumber *offnum;
	int			i;

	/* Update all redirected or moved line pointers */
	offnum = redirected;
	for (i = 0; i < nredirected; i++)
	{
		OffsetNumber fromoff = *offnum++;
		OffsetNumber tooff = *offnum++;
		ItemId		fromlp = PageGetItemId(page, fromoff);

		if (redirect_move)
		{
			/* Physically move the "to" item to the "from" slot */
			ItemId		tolp = PageGetItemId(page, tooff);
			HeapTupleHeader htup;

			*fromlp = *tolp;
			ItemIdSetUnused(tolp);

			/*
			 * Change heap-only status of the tuple because after the line
			 * pointer manipulation, it's no longer a heap-only tuple, but is
			 * directly pointed to by index entries.
			 */
			Assert(ItemIdIsNormal(fromlp));
			htup = (HeapTupleHeader) PageGetItem(page, fromlp);
			Assert(HeapTupleHeaderIsHeapOnly(htup));
			HeapTupleHeaderClearHeapOnly(htup);
		}
		else
		{
			/* Just insert a REDIRECT link at fromoff */
			ItemIdSetRedirect(fromlp, tooff);
		}
	}

	/* Update all now-dead line pointers */
	offnum = nowdead;
	for (i = 0; i < ndead; i++)
	{
		OffsetNumber off = *offnum++;
		ItemId		lp = PageGetItemId(page, off);

		ItemIdSetDead(lp);
	}

	/* Update all now-unused line pointers */
	offnum = nowunused;
	for (i = 0; i < nunused; i++)
	{
		OffsetNumber off = *offnum++;
		ItemId		lp = PageGetItemId(page, off);

		ItemIdSetUnused(lp);
	}

	/*
	 * Finally, repair any fragmentation, and update the page's hint bit about
	 * whether it has free pointers.
	 */
	PageRepairFragmentation(page);
}


/*
 * For all items in this page, find their respective root line pointers.
 * If item k is part of a HOT-chain with root at item j, then we set
 * root_offsets[k - 1] = j.
 *
 * The passed-in root_offsets array must have MaxHeapTuplesPerPage entries.
 * We zero out all unused entries.
 *
 * The function must be called with at least share lock on the buffer, to
 * prevent concurrent prune operations.
 *
 * Note: The information collected here is valid only as long as the caller
 * holds a pin on the buffer. Once pin is released, a tuple might be pruned
 * and reused by a completely unrelated tuple.
 */
void
heap_get_root_tuples(Page page, OffsetNumber *root_offsets)
{
	OffsetNumber offnum,
				maxoff;

	MemSet(root_offsets, 0, MaxHeapTuplesPerPage * sizeof(OffsetNumber));

	maxoff = PageGetMaxOffsetNumber(page);
	for (offnum = FirstOffsetNumber; offnum <= maxoff; offnum++)
	{
		ItemId		lp = PageGetItemId(page, offnum);
		HeapTupleHeader htup;
		OffsetNumber nextoffnum;
		TransactionId priorXmax;

		/* skip unused and dead items */
		if (!ItemIdIsUsed(lp) || ItemIdIsDead(lp))
			continue;

		if (ItemIdIsNormal(lp))
		{
			htup = (HeapTupleHeader) PageGetItem(page, lp);

			/*
			 * Check if this tuple is part of a HOT-chain rooted at some other
			 * tuple. If so, skip it for now; we'll process it when we find
			 * its root.
			 */
			if (HeapTupleHeaderIsHeapOnly(htup))
				continue;

			/*
			 * This is either a plain tuple or the root of a HOT-chain.
			 * Remember it in the mapping.
			 */
			root_offsets[offnum - 1] = offnum;

			/* If it's not the start of a HOT-chain, we're done with it */
			if (!HeapTupleHeaderIsHotUpdated(htup))
				continue;

			/* Set up to scan the HOT-chain */
			nextoffnum = ItemPointerGetOffsetNumber(&htup->t_ctid);
			priorXmax = HeapTupleHeaderGetXmax(htup);
		}
		else
		{
			/* Must be a redirect item. We do not set its root_offsets entry */
			Assert(ItemIdIsRedirected(lp));
			/* Set up to scan the HOT-chain */
			nextoffnum = ItemIdGetRedirect(lp);
			priorXmax = InvalidTransactionId;
		}

		/*
		 * Now follow the HOT-chain and collect other tuples in the chain.
		 *
		 * Note: Even though this is a nested loop, the complexity of the
		 * function is O(N) because a tuple in the page should be visited not
		 * more than twice, once in the outer loop and once in HOT-chain
		 * chases.
		 */
		for (;;)
		{
			lp = PageGetItemId(page, nextoffnum);

			/* Check for broken chains */
			if (!ItemIdIsNormal(lp))
				break;

			htup = (HeapTupleHeader) PageGetItem(page, lp);

			if (TransactionIdIsValid(priorXmax) &&
				!TransactionIdEquals(priorXmax, HeapTupleHeaderGetXmin(htup)))
				break;

			/* Remember the root line pointer for this item */
			root_offsets[nextoffnum - 1] = offnum;

			/* Advance to next chain member, if any */
			if (!HeapTupleHeaderIsHotUpdated(htup))
				break;

			nextoffnum = ItemPointerGetOffsetNumber(&htup->t_ctid);
			priorXmax = HeapTupleHeaderGetXmax(htup);
		}
	}
}