nbtsort.c

来自「PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统」· C语言 代码 · 共 835 行 · 第 1/2 页

/*-------------------------------------------------------------------------
 *
 * nbtsort.c
 *		Build a btree from sorted input by loading leaf pages sequentially.
 *
 * NOTES
 *
 * We use tuplesort.c to sort the given index tuples into order.
 * Then we scan the index tuples in order and build the btree pages
 * for each level.	We load source tuples into leaf-level pages.
 * Whenever we fill a page at one level, we add a link to it to its
 * parent level (starting a new parent level if necessary).  When
 * done, we write out each final page on each level, adding it to
 * its parent level.  When we have only one page on a level, it must be
 * the root -- it can be attached to the btree metapage and we are done.
 *
 * This code is moderately slow (~10% slower) compared to the regular
 * btree (insertion) build code on sorted or well-clustered data.  On
 * random data, however, the insertion build code is unusable -- the
 * difference on a 60MB heap is a factor of 15 because the random
 * probes into the btree thrash the buffer pool.  (NOTE: the above
 * "10%" estimate is probably obsolete, since it refers to an old and
 * not very good external sort implementation that used to exist in
 * this module.  tuplesort.c is almost certainly faster.)
 *
 * It is not wise to pack the pages entirely full, since then *any*
 * insertion would cause a split (and not only of the leaf page; the need
 * for a split would cascade right up the tree).  The steady-state load
 * factor for btrees is usually estimated at 70%.  We choose to pack leaf
 * pages to 90% and upper pages to 70%.  This gives us reasonable density
 * (there aren't many upper pages if the keys are reasonable-size) without
 * incurring a lot of cascading splits during early insertions.
 *
 * Formerly the index pages being built were kept in shared buffers, but
 * that is of no value (since other backends have no interest in them yet)
 * and it created locking problems for CHECKPOINT, because the upper-level
 * pages were held exclusive-locked for long periods.  Now we just build
 * the pages in local memory and smgrwrite() them as we finish them.  They
 * will need to be re-read into shared buffers on first use after the build
 * finishes.
 *
 * Since the index will never be used unless it is completely built,
 * from a crash-recovery point of view there is no need to WAL-log the
 * steps of the build.	After completing the index build, we can just sync
 * the whole file to disk using smgrimmedsync() before exiting this module.
 * This can be seen to be sufficient for crash recovery by considering that
 * it's effectively equivalent to what would happen if a CHECKPOINT occurred
 * just after the index build.	However, it is clearly not sufficient if the
 * DBA is using the WAL log for PITR or replication purposes, since another
 * machine would not be able to reconstruct the index from WAL.  Therefore,
 * we log the completed index pages to WAL if and only if WAL archiving is
 * active.
 *
 *
 * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsort.c,v 1.95.2.3 2006/03/10 20:18:25 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/nbtree.h"
#include "access/xlog.h"
#include "miscadmin.h"
#include "storage/smgr.h"
#include "utils/tuplesort.h"


/*
 * Status record for spooling/sorting phase.  (Note we may have two of
 * these due to the special requirements for uniqueness-checking with
 * dead tuples.)
 */
struct BTSpool
{
	Tuplesortstate *sortstate;	/* state data for tuplesort.c */
	Relation	index;
	bool		isunique;
};

/*
 * Status record for a btree page being built.	We have one of these
 * for each active tree level.
 *
 * The reason we need to store a copy of the minimum key is that we'll
 * need to propagate it to the parent node when this page is linked
 * into its parent.  However, if the page is not a leaf page, the first
 * entry on the page doesn't need to contain a key, so we will not have
 * stored the key itself on the page.  (You might think we could skip
 * copying the minimum key on leaf pages, but actually we must have a
 * writable copy anyway because we'll poke the page's address into it
 * before passing it up to the parent...)
 */
typedef struct BTPageState
{
	Page		btps_page;		/* workspace for page building */
	BlockNumber btps_blkno;		/* block # to write this page at */
	BTItem		btps_minkey;	/* copy of minimum key (first item) on page */
	OffsetNumber btps_lastoff;	/* last item offset loaded */
	uint32		btps_level;		/* tree level (0 = leaf) */
	Size		btps_full;		/* "full" if less than this much free space */
	struct BTPageState *btps_next;		/* link to parent level, if any */
} BTPageState;

/*
 * Overall status record for index writing phase.
 */
typedef struct BTWriteState
{
	Relation	index;
	bool		btws_use_wal;	/* dump pages to WAL? */
	BlockNumber btws_pages_alloced;		/* # pages allocated */
	BlockNumber btws_pages_written;		/* # pages written out */
	Page		btws_zeropage;	/* workspace for filling zeroes */
} BTWriteState;


#define BTITEMSZ(btitem) \
	((btitem) ? \
	 (IndexTupleDSize((btitem)->bti_itup) + \
	  (sizeof(BTItemData) - sizeof(IndexTupleData))) : \
	 0)


static Page _bt_blnewpage(uint32 level);
static BTPageState *_bt_pagestate(BTWriteState *wstate, uint32 level);
static void _bt_slideleft(Page page);
static void _bt_sortaddtup(Page page, Size itemsize,
			   BTItem btitem, OffsetNumber itup_off);
static void _bt_buildadd(BTWriteState *wstate, BTPageState *state, BTItem bti);
static void _bt_uppershutdown(BTWriteState *wstate, BTPageState *state);
static void _bt_load(BTWriteState *wstate,
		 BTSpool *btspool, BTSpool *btspool2);


/*
 * Interface routines
 */


/*
 * create and initialize a spool structure
 */
BTSpool *
_bt_spoolinit(Relation index, bool isunique, bool isdead)
{
	BTSpool    *btspool = (BTSpool *) palloc0(sizeof(BTSpool));
	int			btKbytes;

	btspool->index = index;
	btspool->isunique = isunique;

	/*
	 * We size the sort area as maintenance_work_mem rather than work_mem to
	 * speed index creation.  This should be OK since a single backend can't
	 * run multiple index creations in parallel.  Note that creation of a
	 * unique index actually requires two BTSpool objects.	We expect that the
	 * second one (for dead tuples) won't get very full, so we give it only
	 * work_mem.
	 */
	btKbytes = isdead ? work_mem : maintenance_work_mem;
	btspool->sortstate = tuplesort_begin_index(index, isunique,
											   btKbytes, false);

	/*
	 * Currently, tuplesort provides sort functions on IndexTuples. If we kept
	 * anything in a BTItem other than a regular IndexTuple, we'd need to
	 * modify tuplesort to understand BTItems as such.
	 */
	Assert(sizeof(BTItemData) == sizeof(IndexTupleData));

	return btspool;
}

/*
 * clean up a spool structure and its substructures.
 */
void
_bt_spooldestroy(BTSpool *btspool)
{
	tuplesort_end(btspool->sortstate);
	pfree(btspool);
}

/*
 * spool a btitem into the sort file.
 */
void
_bt_spool(BTItem btitem, BTSpool *btspool)
{
	/* A BTItem is really just an IndexTuple */
	tuplesort_puttuple(btspool->sortstate, (void *) btitem);
}

/*
 * given a spool loaded by successive calls to _bt_spool,
 * create an entire btree.
 */
void
_bt_leafbuild(BTSpool *btspool, BTSpool *btspool2)
{
	BTWriteState wstate;

#ifdef BTREE_BUILD_STATS
	if (log_btree_build_stats)
	{
		ShowUsage("BTREE BUILD (Spool) STATISTICS");
		ResetUsage();
	}
#endif   /* BTREE_BUILD_STATS */

	tuplesort_performsort(btspool->sortstate);
	if (btspool2)
		tuplesort_performsort(btspool2->sortstate);

	wstate.index = btspool->index;

	/*
	 * We need to log index creation in WAL iff WAL archiving is enabled AND
	 * it's not a temp index.
	 */
	wstate.btws_use_wal = XLogArchivingActive() && !wstate.index->rd_istemp;

	/* reserve the metapage */
	wstate.btws_pages_alloced = BTREE_METAPAGE + 1;
	wstate.btws_pages_written = 0;
	wstate.btws_zeropage = NULL;	/* until needed */

	_bt_load(&wstate, btspool, btspool2);
}


/*
 * Internal routines.
 */


/*
 * allocate workspace for a new, clean btree page, not linked to any siblings.
 */
static Page
_bt_blnewpage(uint32 level)
{
	Page		page;
	BTPageOpaque opaque;

	page = (Page) palloc(BLCKSZ);

	/* Zero the page and set up standard page header info */
	_bt_pageinit(page, BLCKSZ);

	/* Initialize BT opaque state */
	opaque = (BTPageOpaque) PageGetSpecialPointer(page);
	opaque->btpo_prev = opaque->btpo_next = P_NONE;
	opaque->btpo.level = level;
	opaque->btpo_flags = (level > 0) ? 0 : BTP_LEAF;

	/* Make the P_HIKEY line pointer appear allocated */
	((PageHeader) page)->pd_lower += sizeof(ItemIdData);

	return page;
}

/*
 * emit a completed btree page, and release the working storage.
 */
static void
_bt_blwritepage(BTWriteState *wstate, Page page, BlockNumber blkno)
{
	/* Ensure rd_smgr is open (could have been closed by relcache flush!) */
	RelationOpenSmgr(wstate->index);

	/* XLOG stuff */
	if (wstate->btws_use_wal)
	{
		/* We use the heap NEWPAGE record type for this */
		xl_heap_newpage xlrec;
		XLogRecPtr	recptr;
		XLogRecData rdata[2];

		/* NO ELOG(ERROR) from here till newpage op is logged */
		START_CRIT_SECTION();

		xlrec.node = wstate->index->rd_node;
		xlrec.blkno = blkno;

		rdata[0].data = (char *) &xlrec;
		rdata[0].len = SizeOfHeapNewpage;
		rdata[0].buffer = InvalidBuffer;
		rdata[0].next = &(rdata[1]);

		rdata[1].data = (char *) page;
		rdata[1].len = BLCKSZ;
		rdata[1].buffer = InvalidBuffer;
		rdata[1].next = NULL;

		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_NEWPAGE, rdata);

		PageSetLSN(page, recptr);
		PageSetTLI(page, ThisTimeLineID);

		END_CRIT_SECTION();
	}
	else
	{
		/* Leave the page LSN zero if not WAL-logged, but set TLI anyway */
		PageSetTLI(page, ThisTimeLineID);
	}

	/*
	 * If we have to write pages nonsequentially, fill in the space with
	 * zeroes until we come back and overwrite.  This is not logically
	 * necessary on standard Unix filesystems (unwritten space will read as
	 * zeroes anyway), but it should help to avoid fragmentation. The dummy
	 * pages aren't WAL-logged though.
	 */
	while (blkno > wstate->btws_pages_written)
	{
		if (!wstate->btws_zeropage)
			wstate->btws_zeropage = (Page) palloc0(BLCKSZ);
		smgrwrite(wstate->index->rd_smgr, wstate->btws_pages_written++,
				  (char *) wstate->btws_zeropage,
				  true);
	}

	/*
	 * Now write the page.	We say isTemp = true even if it's not a temp
	 * index, because there's no need for smgr to schedule an fsync for this
	 * write; we'll do it ourselves before ending the build.
	 */
	smgrwrite(wstate->index->rd_smgr, blkno, (char *) page, true);

	if (blkno == wstate->btws_pages_written)
		wstate->btws_pages_written++;

	pfree(page);
}

/*
 * allocate and initialize a new BTPageState.  the returned structure
 * is suitable for immediate use by _bt_buildadd.
 */
static BTPageState *
_bt_pagestate(BTWriteState *wstate, uint32 level)
{
	BTPageState *state = (BTPageState *) palloc0(sizeof(BTPageState));

	/* create initial page for level */
	state->btps_page = _bt_blnewpage(level);

	/* and assign it a page position */
	state->btps_blkno = wstate->btws_pages_alloced++;

	state->btps_minkey = NULL;
	/* initialize lastoff so first item goes into P_FIRSTKEY */
	state->btps_lastoff = P_HIKEY;
	state->btps_level = level;
	/* set "full" threshold based on level.  See notes at head of file. */
	if (level > 0)
		state->btps_full = (PageGetPageSize(state->btps_page) * 3) / 10;
	else
		state->btps_full = PageGetPageSize(state->btps_page) / 10;
	/* no parent level, yet */
	state->btps_next = NULL;

	return state;
}

/*
 * slide an array of ItemIds back one slot (from P_FIRSTKEY to
 * P_HIKEY, overwriting P_HIKEY).  we need to do this when we discover
 * that we have built an ItemId array in what has turned out to be a
 * P_RIGHTMOST page.
 */
static void
_bt_slideleft(Page page)
{
	OffsetNumber off;
	OffsetNumber maxoff;
	ItemId		previi;
	ItemId		thisii;

	if (!PageIsEmpty(page))
	{
		maxoff = PageGetMaxOffsetNumber(page);
		previi = PageGetItemId(page, P_HIKEY);
		for (off = P_FIRSTKEY; off <= maxoff; off = OffsetNumberNext(off))
		{
			thisii = PageGetItemId(page, off);
			*previi = *thisii;
			previi = thisii;
		}
		((PageHeader) page)->pd_lower -= sizeof(ItemIdData);
	}
}

/*
 * Add an item to a page being built.
 *
 * The main difference between this routine and a bare PageAddItem call
 * is that this code knows that the leftmost data item on a non-leaf
 * btree page doesn't need to have a key.  Therefore, it strips such
 * items down to just the item header.
 *
 * This is almost like nbtinsert.c's _bt_pgaddtup(), but we can't use
 * that because it assumes that P_RIGHTMOST() will return the correct
 * answer for the page.  Here, we don't know yet if the page will be
 * rightmost.  Offset P_FIRSTKEY is always the first data key.
 */
static void
_bt_sortaddtup(Page page,
			   Size itemsize,
			   BTItem btitem,
			   OffsetNumber itup_off)