mp_fget.c

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/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996-2004
 *	Sleepycat Software.  All rights reserved.
 *
 * $Id: mp_fget.c,v 11.96 2004/10/15 16:59:42 bostic Exp $
 */

#include "db_config.h"

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>

#include <string.h>
#endif

#include "db_int.h"
#include "dbinc/db_shash.h"
#include "dbinc/log.h"
#include "dbinc/mp.h"

/*
 * __memp_fget_pp --
 *	DB_MPOOLFILE->get pre/post processing.
 *
 * PUBLIC: int __memp_fget_pp
 * PUBLIC:     __P((DB_MPOOLFILE *, db_pgno_t *, u_int32_t, void *));
 */
int
__memp_fget_pp(dbmfp, pgnoaddr, flags, addrp)
	DB_MPOOLFILE *dbmfp;
	db_pgno_t *pgnoaddr;
	u_int32_t flags;
	void *addrp;
{
	DB_ENV *dbenv;
	int rep_check, ret;

	dbenv = dbmfp->dbenv;

	PANIC_CHECK(dbenv);
	MPF_ILLEGAL_BEFORE_OPEN(dbmfp, "DB_MPOOLFILE->get");

	/*
	 * Validate arguments.
	 *
	 * !!!
	 * Don't test for DB_MPOOL_CREATE and DB_MPOOL_NEW flags for readonly
	 * files here, and create non-existent pages in readonly files if the
	 * flags are set, later.  The reason is that the hash access method
	 * wants to get empty pages that don't really exist in readonly files.
	 * The only alternative is for hash to write the last "bucket" all the
	 * time, which we don't want to do because one of our big goals in life
	 * is to keep database files small.  It's sleazy as hell, but we catch
	 * any attempt to actually write the file in memp_fput().
	 */
#define	OKFLAGS		(DB_MPOOL_CREATE | DB_MPOOL_LAST | DB_MPOOL_NEW)
	if (flags != 0) {
		if ((ret = __db_fchk(dbenv, "memp_fget", flags, OKFLAGS)) != 0)
			return (ret);

		switch (flags) {
		case DB_MPOOL_CREATE:
		case DB_MPOOL_LAST:
		case DB_MPOOL_NEW:
			break;
		default:
			return (__db_ferr(dbenv, "memp_fget", 1));
		}
	}

	rep_check = IS_ENV_REPLICATED(dbenv) ? 1 : 0;
	if (rep_check)
		__op_rep_enter(dbenv);
	ret = __memp_fget(dbmfp, pgnoaddr, flags, addrp);
	/*
	 * We only decrement the count in op_rep_exit if the operation fails.
	 * Otherwise the count will be decremented when the page is no longer
	 * pinned in memp_fput.
	 */
	if (ret != 0 && rep_check)
		__op_rep_exit(dbenv);
	return (ret);
}

/*
 * __memp_fget --
 *	Get a page from the file.
 *
 * PUBLIC: int __memp_fget
 * PUBLIC:     __P((DB_MPOOLFILE *, db_pgno_t *, u_int32_t, void *));
 */
int
__memp_fget(dbmfp, pgnoaddr, flags, addrp)
	DB_MPOOLFILE *dbmfp;
	db_pgno_t *pgnoaddr;
	u_int32_t flags;
	void *addrp;
{
	enum { FIRST_FOUND, FIRST_MISS, SECOND_FOUND, SECOND_MISS } state;
	BH *alloc_bhp, *bhp;
	DB_ENV *dbenv;
	DB_MPOOL *dbmp;
	DB_MPOOL_HASH *hp;
	MPOOL *c_mp, *mp;
	MPOOLFILE *mfp;
	roff_t mf_offset;
	u_int32_t n_cache, st_hsearch;
	int b_incr, extending, first, ret;

	*(void **)addrp = NULL;

	dbenv = dbmfp->dbenv;
	dbmp = dbenv->mp_handle;

	c_mp = NULL;
	mp = dbmp->reginfo[0].primary;
	mfp = dbmfp->mfp;
	mf_offset = R_OFFSET(dbmp->reginfo, mfp);
	alloc_bhp = bhp = NULL;
	hp = NULL;
	b_incr = extending = ret = 0;

	switch (flags) {
	case DB_MPOOL_LAST:
		/* Get the last page number in the file. */
		R_LOCK(dbenv, dbmp->reginfo);
		*pgnoaddr = mfp->last_pgno;
		R_UNLOCK(dbenv, dbmp->reginfo);
		break;
	case DB_MPOOL_NEW:
		/*
		 * If always creating a page, skip the first search
		 * of the hash bucket.
		 */
		goto alloc;
	case DB_MPOOL_CREATE:
	default:
		break;
	}

	/*
	 * If mmap'ing the file and the page is not past the end of the file,
	 * just return a pointer.  We can't use R_ADDR here: this is an offset
	 * into an mmap'd file, not a shared region, and doesn't change for
	 * private environments.
	 *
	 * The page may be past the end of the file, so check the page number
	 * argument against the original length of the file.  If we previously
	 * returned pages past the original end of the file, last_pgno will
	 * have been updated to match the "new" end of the file, and checking
	 * against it would return pointers past the end of the mmap'd region.
	 *
	 * If another process has opened the file for writing since we mmap'd
	 * it, we will start playing the game by their rules, i.e. everything
	 * goes through the cache.  All pages previously returned will be safe,
	 * as long as the correct locking protocol was observed.
	 *
	 * We don't discard the map because we don't know when all of the
	 * pages will have been discarded from the process' address space.
	 * It would be possible to do so by reference counting the open
	 * pages from the mmap, but it's unclear to me that it's worth it.
	 */
	if (dbmfp->addr != NULL &&
	    F_ISSET(mfp, MP_CAN_MMAP) && *pgnoaddr <= mfp->orig_last_pgno) {
		*(void **)addrp = (u_int8_t *)dbmfp->addr +
		    (*pgnoaddr * mfp->stat.st_pagesize);
		++mfp->stat.st_map;
		return (0);
	}

hb_search:
	/*
	 * Determine the cache and hash bucket where this page lives and get
	 * local pointers to them.  Reset on each pass through this code, the
	 * page number can change.
	 */
	n_cache = NCACHE(mp, mf_offset, *pgnoaddr);
	c_mp = dbmp->reginfo[n_cache].primary;
	hp = R_ADDR(&dbmp->reginfo[n_cache], c_mp->htab);
	hp = &hp[NBUCKET(c_mp, mf_offset, *pgnoaddr)];

	/* Search the hash chain for the page. */
retry:	st_hsearch = 0;
	MUTEX_LOCK(dbenv, &hp->hash_mutex);
	for (bhp = SH_TAILQ_FIRST(&hp->hash_bucket, __bh);
	    bhp != NULL; bhp = SH_TAILQ_NEXT(bhp, hq, __bh)) {
		++st_hsearch;
		if (bhp->pgno != *pgnoaddr || bhp->mf_offset != mf_offset)
			continue;

		/*
		 * Increment the reference count.  We may discard the hash
		 * bucket lock as we evaluate and/or read the buffer, so we
		 * need to ensure it doesn't move and its contents remain
		 * unchanged.
		 */
		if (bhp->ref == UINT16_MAX) {
			MUTEX_UNLOCK(dbenv, &hp->hash_mutex);

			__db_err(dbenv,
			    "%s: page %lu: reference count overflow",
			    __memp_fn(dbmfp), (u_long)bhp->pgno);
			ret = __db_panic(dbenv, EINVAL);
			goto err;
		}
		++bhp->ref;
		b_incr = 1;

		/*
		 * BH_LOCKED --
		 * I/O is in progress or sync is waiting on the buffer to write
		 * it.  Because we've incremented the buffer reference count,
		 * we know the buffer can't move.  Unlock the bucket lock, wait
		 * for the buffer to become available, reacquire the bucket.
		 */
		for (first = 1; F_ISSET(bhp, BH_LOCKED) &&
		    !F_ISSET(dbenv, DB_ENV_NOLOCKING); first = 0) {
			/*
			 * If someone is trying to sync this buffer and the
			 * buffer is hot, they may never get in.  Give up
			 * and try again.
			 */
			if (!first && bhp->ref_sync != 0) {
				--bhp->ref;
				b_incr = 0;
				MUTEX_UNLOCK(dbenv, &hp->hash_mutex);
				__os_yield(dbenv, 1);
				goto retry;
			}

			MUTEX_UNLOCK(dbenv, &hp->hash_mutex);
			/*
			 * Explicitly yield the processor if not the first pass
			 * through this loop -- if we don't, we might run to the
			 * end of our CPU quantum as we will simply be swapping
			 * between the two locks.
			 */
			if (!first)
				__os_yield(dbenv, 1);

			MUTEX_LOCK(dbenv, &bhp->mutex);
			/* Wait for I/O to finish... */
			MUTEX_UNLOCK(dbenv, &bhp->mutex);
			MUTEX_LOCK(dbenv, &hp->hash_mutex);
		}

		++mfp->stat.st_cache_hit;
		break;
	}

	/*
	 * Update the hash bucket search statistics -- do now because our next
	 * search may be for a different bucket.
	 */
	++c_mp->stat.st_hash_searches;
	if (st_hsearch > c_mp->stat.st_hash_longest)
		c_mp->stat.st_hash_longest = st_hsearch;
	c_mp->stat.st_hash_examined += st_hsearch;

	/*
	 * There are 4 possible paths to this location:
	 *
	 * FIRST_MISS:
	 *	Didn't find the page in the hash bucket on our first pass:
	 *	bhp == NULL, alloc_bhp == NULL
	 *
	 * FIRST_FOUND:
	 *	Found the page in the hash bucket on our first pass:
	 *	bhp != NULL, alloc_bhp == NULL
	 *
	 * SECOND_FOUND:
	 *	Didn't find the page in the hash bucket on the first pass,
	 *	allocated space, and found the page in the hash bucket on
	 *	our second pass:
	 *	bhp != NULL, alloc_bhp != NULL
	 *
	 * SECOND_MISS:
	 *	Didn't find the page in the hash bucket on the first pass,
	 *	allocated space, and didn't find the page in the hash bucket
	 *	on our second pass:
	 *	bhp == NULL, alloc_bhp != NULL
	 */
	state = bhp == NULL ?
	    (alloc_bhp == NULL ? FIRST_MISS : SECOND_MISS) :
	    (alloc_bhp == NULL ? FIRST_FOUND : SECOND_FOUND);
	switch (state) {
	case FIRST_FOUND:
		/*
		 * If we are to free the buffer, then this had better
		 * be the only reference. If so, just free the buffer.
		 * If not, complain and get out.
		 */
		if (flags == DB_MPOOL_FREE) {
			if (bhp->ref == 1) {
				__memp_bhfree(dbmp, hp, bhp, BH_FREE_FREEMEM);
				return (0);
			}
			__db_err(dbenv,
			    "File %s: freeing pinned buffer for page %lu",
				__memp_fns(dbmp, mfp), (u_long)*pgnoaddr);
			ret = __db_panic(dbenv, EINVAL);
			goto err;
		}

		/* We found the buffer in our first check -- we're done. */
		break;
	case FIRST_MISS:
		/*
		 * We didn't find the buffer in our first check.  Figure out
		 * if the page exists, and allocate structures so we can add
		 * the page to the buffer pool.
		 */
		MUTEX_UNLOCK(dbenv, &hp->hash_mutex);

		/*
		 * The buffer is not in the pool, so we don't need to free it.
		 */
		if (flags == DB_MPOOL_FREE)
			return (0);

alloc:		/*
		 * If DB_MPOOL_NEW is set, we have to allocate a page number.
		 * If neither DB_MPOOL_CREATE or DB_MPOOL_CREATE is set, then
		 * it's an error to try and get a page past the end of file.
		 */
		COMPQUIET(n_cache, 0);