/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998, 1999
 *	Sleepycat Software.  All rights reserved.
 */
#include "db_config.h"

#ifndef lint
static const char sccsid[] = "@(#)mp_trickle.c	11.3 (Sleepycat) 9/16/99";
#endif /* not lint */

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

#include <errno.h>
#include <stdlib.h>
#endif

#include "db_int.h"
#include "db_shash.h"
#include "mp.h"

static int CDB___memp_trick __P((DB_ENV *, int, int, int *));

/*
 * CDB_memp_trickle --
 *	Keep a specified percentage of the buffers clean.
 */
int
CDB_memp_trickle(dbenv, pct, nwrotep)
	DB_ENV *dbenv;
	int pct, *nwrotep;
{
	DB_MPOOL *dbmp;
	MPOOL *mp;
	u_int32_t i;
	int ret;

	PANIC_CHECK(dbenv);
	ENV_REQUIRES_CONFIG(dbenv, dbenv->mp_handle, DB_INIT_MPOOL);

	dbmp = dbenv->mp_handle;
	mp = dbmp->reginfo.primary;

	if (nwrotep != NULL)
		*nwrotep = 0;

	if (pct < 1 || pct > 100)
		return (EINVAL);

	R_LOCK(dbenv, &dbmp->reginfo);

	/* Loop through the caches... */
	for (ret = 0, i = 0; i < mp->nc_reg; ++i)
		if ((ret = CDB___memp_trick(dbenv, i, pct, nwrotep)) != 0)
			break;

	R_UNLOCK(dbenv, &dbmp->reginfo);
	return (ret);
}

/*
 * CDB___memp_trick --
 *	Trickle a single cache.
 */
static int
CDB___memp_trick(dbenv, ncache, pct, nwrotep)
	DB_ENV *dbenv;
	int ncache, pct, *nwrotep;
{
	BH *bhp;
	DB_MPOOL *dbmp;
	MCACHE *mc;
	MPOOLFILE *mfp;
	db_pgno_t pgno;
	u_long total;
	int ret, wrote;

	dbmp = dbenv->mp_handle;
	mc = dbmp->c_reginfo[ncache].primary;

	/*
	 * If there are sufficient clean buffers, or no buffers or no dirty
	 * buffers, we're done.
	 *
	 * XXX
	 * Using st_page_clean and st_page_dirty is our only choice at the
	 * moment, but it's not as correct as we might like in the presence
	 * of pools with more than one buffer size, as a free 512-byte buffer
	 * isn't the same as a free 8K buffer.
	 */
loop:	total = mc->stat.st_page_clean + mc->stat.st_page_dirty;
	if (total == 0 || mc->stat.st_page_dirty == 0 ||
	    (mc->stat.st_page_clean * 100) / total >= (u_long)pct)
		return (0);

	/* Loop until we write a buffer. */
	for (bhp = SH_TAILQ_FIRST(&mc->bhq, __bh);
	    bhp != NULL; bhp = SH_TAILQ_NEXT(bhp, q, __bh)) {
		if (bhp->ref != 0 ||
		    !F_ISSET(bhp, BH_DIRTY) || F_ISSET(bhp, BH_LOCKED))
			continue;

		mfp = R_ADDR(&dbmp->reginfo, bhp->mf_offset);

		/*
		 * We can't write to temporary files -- see the comment in
		 * mp_bh.c:CDB___memp_bhwrite().
		 */
		if (F_ISSET(mfp, MP_TEMP))
			continue;

		pgno = bhp->pgno;
		if ((ret = CDB___memp_bhwrite(dbmp, mfp, bhp, NULL, &wrote)) != 0)
			return (ret);

		/*
		 * Any process syncing the shared memory buffer pool had better
		 * be able to write to any underlying file.  Be understanding,
		 * but firm, on this point.
		 */
		if (!wrote) {
			CDB___db_err(dbenv, "%s: unable to flush page: %lu",
			    CDB___memp_fns(dbmp, mfp), (u_long)pgno);
			return (EPERM);
		}

		++mc->stat.st_page_trickle;
		if (nwrotep != NULL)
			++*nwrotep;
		goto loop;
	}

	return (0);
}