cpython-source-deps/db/db_dispatch.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996,2008 Oracle.  All rights reserved.
 */
/*
 * Copyright (c) 1995, 1996
 *	The President and Fellows of Harvard University.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Margo Seltzer.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $Id: db_dispatch.c 63573 2008-05-23 21:43:21Z trent.nelson $
 */

#include "db_config.h"

#include "db_int.h"
#include "dbinc/db_page.h"
#include "dbinc/hash.h"
#include "dbinc/fop.h"
#include "dbinc/lock.h"
#include "dbinc/log.h"
#include "dbinc/mp.h"
#include "dbinc/txn.h"

static int __db_txnlist_find_internal __P((ENV *, DB_TXNHEAD *,
		db_txnlist_type, u_int32_t,  DB_TXNLIST **,
		int, u_int32_t *));

/*
 * __db_dispatch --
 *
 * This is the transaction dispatch function used by the db access methods.
 * It is designed to handle the record format used by all the access
 * methods (the one automatically generated by the db_{h,log,read}.sh
 * scripts in the tools directory).  An application using a different
 * recovery paradigm will supply a different dispatch function to txn_open.
 *
 * PUBLIC: int __db_dispatch __P((ENV *,
 * PUBLIC:     DB_DISTAB *, DBT *, DB_LSN *, db_recops, DB_TXNHEAD *));
 */
int
__db_dispatch(env, dtab, db, lsnp, redo, info)
	ENV *env;		/* The environment. */
	DB_DISTAB *dtab;
	DBT *db;		/* The log record upon which to dispatch. */
	DB_LSN *lsnp;		/* The lsn of the record being dispatched. */
	db_recops redo;		/* Redo this op (or undo it). */
	DB_TXNHEAD *info;	/* Transaction list. */
{
	DB_ENV *dbenv;
	DB_LSN prev_lsn;
	u_int32_t rectype, status, txnid, urectype;
	int make_call, ret;

	dbenv = env->dbenv;
	LOGCOPY_32(env, &rectype, db->data);
	LOGCOPY_32(env, &txnid, (u_int8_t *)db->data + sizeof(rectype));

	make_call = ret = 0;

	/* If we don't have a dispatch table, it's hard to dispatch. */
	DB_ASSERT(env, dtab != NULL);

	/*
	 * If we find a record that is in the user's number space and they
	 * have specified a recovery routine, let them handle it.  If they
	 * didn't specify a recovery routine, then we expect that they've
	 * followed all our rules and registered new recovery functions.
	 */
	switch (redo) {
	case DB_TXN_ABORT:
	case DB_TXN_APPLY:
	case DB_TXN_PRINT:
		make_call = 1;
		break;
	case DB_TXN_OPENFILES:
		/*
		 * We collect all the transactions that have
		 * "begin" records, those with no previous LSN,
		 * so that we do not abort partial transactions.
		 * These are known to be undone, otherwise the
		 * log would not have been freeable.
		 */
		LOGCOPY_TOLSN(env, &prev_lsn, (u_int8_t *)db->data +
		    sizeof(rectype) + sizeof(txnid));
		if (txnid != 0 && prev_lsn.file == 0 && (ret =
		    __db_txnlist_add(env, info, txnid, TXN_OK, NULL)) != 0)
			return (ret);

		/* FALLTHROUGH */
	case DB_TXN_POPENFILES:
		if (rectype == DB___dbreg_register ||
		    rectype == DB___txn_child ||
		    rectype == DB___txn_ckp || rectype == DB___txn_recycle)
			return ((dtab->int_dispatch[rectype])(env,
			    db, lsnp, redo, info));
		break;
	case DB_TXN_BACKWARD_ROLL:
		/*
		 * Running full recovery in the backward pass. In general,
		 * we only process records during this pass that belong
		 * to aborted transactions.  Unfortunately, there are several
		 * exceptions:
		 * 1. If this is a meta-record, one not associated with
		 *    a transaction, then we must always process it.
		 * 2. If this is a transaction commit/abort, we must
		 *    always process it, so that we know the status of
		 *    every transaction.
		 * 3. If this is a child commit, we need to process it
		 *    because the outcome of the child transaction depends
		 *    on the outcome of the parent.
		 * 4. If this is a dbreg_register record, we must always
		 *    process is because they contain non-transactional
		 *    closes that must be properly handled.
		 * 5. If this is a noop, we must always undo it so that we
		 *    properly handle any aborts before a file was closed.
		 * 6. If this a file remove, we need to process it to
		 *    determine if the on-disk file is the same as the
		 *    one being described.
		 */
		switch (rectype) {
		/*
		 * These either do not belong to a transaction or (regop)
		 * must be processed regardless of the status of the
		 * transaction.
		 */
		case DB___txn_regop:
		case DB___txn_recycle:
		case DB___txn_ckp:
			make_call = 1;
			break;
		/*
		 * These belong to a transaction whose status must be
		 * checked.
		 */
		case DB___txn_child:
		case DB___db_noop:
		case DB___fop_file_remove:
		case DB___dbreg_register:
			make_call = 1;

			/* FALLTHROUGH */
		default:
			if (txnid == 0)
				break;

			ret = __db_txnlist_find(env, info, txnid, &status);

			/* If not found, this is an incomplete abort.  */
			if (ret == DB_NOTFOUND)
				return (__db_txnlist_add(env,
				    info, txnid, TXN_IGNORE, lsnp));
			if (ret != 0)
				return (ret);

			/*
			 * If we ignore the transaction, ignore the operation
			 * UNLESS this is a child commit in which case we need
			 * to make sure that the child also gets marked as
			 * ignore.
			 */
			if (status == TXN_IGNORE && rectype != DB___txn_child) {
				make_call = 0;
				break;
			}
			if (status == TXN_COMMIT)
				break;

			/* Set make_call in case we came through default */
			make_call = 1;
			if (status == TXN_OK &&
			    (ret = __db_txnlist_update(env,
			    info, txnid, rectype == DB___txn_xa_regop ?
			    TXN_PREPARE : TXN_ABORT, NULL, &status, 0)) != 0)
				return (ret);
		}
		break;
	case DB_TXN_FORWARD_ROLL:
		/*
		 * In the forward pass, if we haven't seen the transaction,
		 * do nothing, else recover it.
		 *
		 * We need to always redo DB___db_noop records, so that we
		 * properly handle any commits after the file was closed.
		 */
		switch (rectype) {
		case DB___txn_recycle:
		case DB___txn_ckp:
		case DB___db_noop:
		case DB___dbreg_register:
			make_call = 1;
			break;

		default:
			if (txnid == 0)
				status = 0;
			else {
				ret = __db_txnlist_find(env,
				    info, txnid, &status);

				if (ret == DB_NOTFOUND)
					/* Break out out of if clause. */
					;
				else if (ret != 0)
					return (ret);
				else if (status == TXN_COMMIT) {
					make_call = 1;
					break;
				}
			}

		}
		break;
	default:
		return (__db_unknown_flag(
		    env, "__db_dispatch", (u_int32_t)redo));
	}

	if (make_call) {
		/*
		 * If the debug flag is set then we are logging
		 * records for a non-durable update so that they
		 * may be examined for diagnostic purposes.
		 * So only make the call if we are printing,
		 * otherwise we need to extract the previous
		 * lsn so undo will work properly.
		 */
		if (rectype & DB_debug_FLAG) {
			if (redo == DB_TXN_PRINT)
				rectype &= ~DB_debug_FLAG;
			else {
				LOGCOPY_TOLSN(env, lsnp,
				    (u_int8_t *)db->data +
				    sizeof(rectype) +
				    sizeof(txnid));
				return (0);
			}
		}
		if (rectype >= DB_user_BEGIN) {
			if (dbenv->app_dispatch != NULL)
				return (dbenv->app_dispatch(dbenv,
				    db, lsnp, redo));

			/* No application-specific dispatch */
			urectype = rectype - DB_user_BEGIN;
			if (urectype > dtab->ext_size ||
			    dtab->ext_dispatch[urectype] == NULL) {
				__db_errx(env,
	    "Illegal application-specific record type %lu in log",
				    (u_long)rectype);
				return (EINVAL);
			}
			return ((dtab->ext_dispatch[urectype])(dbenv,
			    db, lsnp, redo));
		} else {
			if (rectype > dtab->int_size ||
			    dtab->int_dispatch[rectype] == NULL) {
				__db_errx(env,
				    "Illegal record type %lu in log",
				    (u_long)rectype);
				return (EINVAL);
			}
			return ((dtab->int_dispatch[rectype])(env,
			    db, lsnp, redo, info));
		}
	}

	return (0);
}

/*
 * __db_add_recovery -- Add recovery functions to the dispatch table.
 *
 * We have two versions of this, an external one and an internal one,
 * because application-specific functions take different arguments
 * for dispatch (ENV versus DB_ENV).
 *
 * This is the external version.
 *
 * PUBLIC: int __db_add_recovery __P((DB_ENV *, DB_DISTAB *,
 * PUBLIC:   int (*)(DB_ENV *, DBT *, DB_LSN *, db_recops), u_int32_t));
 */
int
__db_add_recovery(dbenv, dtab, func, ndx)
	DB_ENV *dbenv;
	DB_DISTAB *dtab;
	int (*func) __P((DB_ENV *, DBT *, DB_LSN *, db_recops));
	u_int32_t ndx;
{
	size_t i, nsize;
	int ret;

	/* Make sure this is an application-specific record. */
	if (ndx < DB_user_BEGIN) {
		__db_errx(dbenv->env,
	 "Attempting to add application-specific record with invalid type %lu",
		    (u_long)ndx);
		return (EINVAL);
	}
	ndx -= DB_user_BEGIN;

	/* Check if we have to grow the table. */
	if (ndx >= dtab->ext_size) {
		nsize = ndx + 40;
		if ((ret =
		    __os_realloc(dbenv->env, nsize *
		    sizeof((dtab->ext_dispatch)[0]), &dtab->ext_dispatch))
		    != 0)
			return (ret);
		for (i = dtab->ext_size; i < nsize; ++i)
			(dtab->ext_dispatch)[i] = NULL;
		dtab->ext_size = nsize;
	}

	(dtab->ext_dispatch)[ndx] = func;
	return (0);
}

/*
 * __db_add_recovery_int --
 *
 * Internal version of dispatch addition function.
 *
 *
 * PUBLIC: int __db_add_recovery_int __P((ENV *, DB_DISTAB *,
 * PUBLIC:   int (*)(ENV *, DBT *, DB_LSN *, db_recops, void *), u_int32_t));
 */
int
__db_add_recovery_int(env, dtab, func, ndx)
	ENV *env;
	DB_DISTAB *dtab;
	int (*func) __P((ENV *, DBT *, DB_LSN *, db_recops, void *));
	u_int32_t ndx;
{
	size_t i, nsize;
	int ret;

	if (ndx >= DB_user_BEGIN) {
		__db_errx(env,
		    "Attempting to add internal record with invalid type %lu",
		    (u_long)ndx);
		return (EINVAL);
	}

	/* Check if we have to grow the table. */
	if (ndx >= dtab->int_size) {
		nsize = ndx + 40;
		if ((ret =
		    __os_realloc(env, nsize * sizeof((dtab->int_dispatch)[0]),
		    &dtab->int_dispatch)) != 0)
			return (ret);
		for (i = dtab->int_size; i < nsize; ++i)
			(dtab->int_dispatch)[i] = NULL;
		dtab->int_size = nsize;
	}

	(dtab->int_dispatch)[ndx] = func;
	return (0);
}

/*
 * __db_txnlist_init --
 *	Initialize transaction linked list.
 *
 * PUBLIC: int __db_txnlist_init __P((ENV *, DB_THREAD_INFO *,
 * PUBLIC:     u_int32_t, u_int32_t, DB_LSN *, DB_TXNHEAD **));
 */
int
__db_txnlist_init(env, ip, low_txn, hi_txn, trunc_lsn, retp)
	ENV *env;
	DB_THREAD_INFO *ip;
	u_int32_t low_txn, hi_txn;
	DB_LSN *trunc_lsn;
	DB_TXNHEAD **retp;
{
	DB_TXNHEAD *headp;
	u_int32_t size, tmp;
	int ret;

	/*
	 * Size a hash table.
	 *	If low is zero then we are being called during rollback
	 * and we need only one slot.
	 *	Hi maybe lower than low if we have recycled txnid's.
	 *	The numbers here are guesses about txn density, we can afford
	 * to look at a few entries in each slot.
	 */
	if (low_txn == 0)
		size = 1;
	else {
		if (hi_txn < low_txn) {
			tmp = hi_txn;
			hi_txn = low_txn;
			low_txn = tmp;
		}
		tmp = hi_txn - low_txn;
		/* See if we wrapped around. */
		if (tmp > (TXN_MAXIMUM - TXN_MINIMUM) / 2)
			tmp = (low_txn - TXN_MINIMUM) + (TXN_MAXIMUM - hi_txn);
		size = tmp / 5;
		if (size < 100)
			size = 100;
	}
	if ((ret = __os_malloc(env,
	    sizeof(DB_TXNHEAD) + size * sizeof(headp->head), &headp)) != 0)
		return (ret);

	memset(headp, 0, sizeof(DB_TXNHEAD) + size * sizeof(headp->head));
	headp->maxid = hi_txn;
	headp->generation = 0;
	headp->nslots = size;
	headp->gen_alloc = 8;
	headp->thread_info = ip;
	if ((ret = __os_malloc(env, headp->gen_alloc *
	    sizeof(headp->gen_array[0]), &headp->gen_array)) != 0) {
		__os_free(env, headp);
		return (ret);
	}
	headp->gen_array[0].generation = 0;
	headp->gen_array[0].txn_min = TXN_MINIMUM;
	headp->gen_array[0].txn_max = TXN_MAXIMUM;
	if (trunc_lsn != NULL) {
		headp->trunc_lsn = *trunc_lsn;
		headp->maxlsn = *trunc_lsn;
	} else {
		ZERO_LSN(headp->trunc_lsn);
		ZERO_LSN(headp->maxlsn);
	}
	ZERO_LSN(headp->ckplsn);

	*retp = headp;
	return (0);
}

#define	FIND_GENERATION(hp, txnid, gen) do {				\
	u_int32_t __i;							\
	for (__i = 0; __i <= (hp)->generation; __i++)			\
		/* The range may wrap around the end. */		\
		if ((hp)->gen_array[__i].txn_min <			\
		    (hp)->gen_array[__i].txn_max ?			\
		    ((txnid) >= (hp)->gen_array[__i].txn_min &&		\
		    (txnid) <= (hp)->gen_array[__i].txn_max) :		\
		    ((txnid) >= (hp)->gen_array[__i].txn_min ||		\
		    (txnid) <= (hp)->gen_array[__i].txn_max))		\
			break;						\
	DB_ASSERT(env, __i <= (hp)->generation);			\
	gen = (hp)->gen_array[__i].generation;				\
} while (0)

/*
 * __db_txnlist_add --
 *	Add an element to our transaction linked list.
 *
 * PUBLIC: int __db_txnlist_add __P((ENV *,
 * PUBLIC:     DB_TXNHEAD *, u_int32_t, u_int32_t, DB_LSN *));
 */
int
__db_txnlist_add(env, hp, txnid, status, lsn)
	ENV *env;
	DB_TXNHEAD *hp;
	u_int32_t txnid, status;
	DB_LSN *lsn;
{
	DB_TXNLIST *elp;
	int ret;

	if ((ret = __os_malloc(env, sizeof(DB_TXNLIST), &elp)) != 0)
		return (ret);

	LIST_INSERT_HEAD(&hp->head[DB_TXNLIST_MASK(hp, txnid)], elp, links);

	/* Find the most recent generation containing this ID */
	FIND_GENERATION(hp, txnid, elp->u.t.generation);
	elp->type = TXNLIST_TXNID;
	elp->u.t.txnid = txnid;
	elp->u.t.status = status;
	if (txnid > hp->maxid)
		hp->maxid = txnid;
	if (lsn != NULL && IS_ZERO_LSN(hp->maxlsn) && status == TXN_COMMIT)
		hp->maxlsn = *lsn;

	DB_ASSERT(env, lsn == NULL ||
	    status != TXN_COMMIT || LOG_COMPARE(&hp->maxlsn, lsn) >= 0);

	return (0);
}

/*
 * __db_txnlist_remove --
 *	Remove an element from our transaction linked list.
 *
 * PUBLIC: int __db_txnlist_remove __P((ENV *, DB_TXNHEAD *, u_int32_t));
 */
int
__db_txnlist_remove(env, hp, txnid)
	ENV *env;
	DB_TXNHEAD *hp;
	u_int32_t txnid;
{
	DB_TXNLIST *entry;
	u_int32_t status;

	return (__db_txnlist_find_internal(env,
	    hp, TXNLIST_TXNID, txnid, &entry, 1, &status));
}

/*
 * __db_txnlist_ckp --
 *	Used to record the maximum checkpoint that will be retained
 * after recovery.  Typically this is simply the max checkpoint, but
 * if we are doing client replication recovery or timestamp-based
 * recovery, we are going to virtually truncate the log and we need
 * to retain the last checkpoint before the truncation point.
 *
 * PUBLIC: void __db_txnlist_ckp __P((ENV *, DB_TXNHEAD *, DB_LSN *));
 */
void
__db_txnlist_ckp(env, hp, ckp_lsn)
	ENV *env;
	DB_TXNHEAD *hp;
	DB_LSN *ckp_lsn;
{

	COMPQUIET(env, NULL);

	if (IS_ZERO_LSN(hp->ckplsn) && !IS_ZERO_LSN(hp->maxlsn) &&
	    LOG_COMPARE(&hp->maxlsn, ckp_lsn) >= 0)
		hp->ckplsn = *ckp_lsn;
}

/*
 * __db_txnlist_end --
 *	Discard transaction linked list.
 *
 * PUBLIC: void __db_txnlist_end __P((ENV *, DB_TXNHEAD *));
 */
void
__db_txnlist_end(env, hp)
	ENV *env;
	DB_TXNHEAD *hp;
{
	u_int32_t i;
	DB_TXNLIST *p;

	if (hp == NULL)
		return;

	for (i = 0; i < hp->nslots; i++)
		while (hp != NULL && (p = LIST_FIRST(&hp->head[i])) != NULL) {
			switch (p->type) {
			case TXNLIST_LSN:
				__os_free(env, p->u.l.lsn_stack);
				break;
			case TXNLIST_DELETE:
			case TXNLIST_TXNID:
			default:
				/*
				 * Possibly an incomplete DB_TXNLIST; just
				 * free it.
				 */
				break;
			}
			LIST_REMOVE(p, links);
			__os_free(env, p);
		}

	if (hp->gen_array != NULL)
		__os_free(env, hp->gen_array);
	__os_free(env, hp);
}

/*
 * __db_txnlist_find --
 *	Checks to see if a txnid with the current generation is in the
 *	txnid list.  This returns DB_NOTFOUND if the item isn't in the
 *	list otherwise it returns (like __db_txnlist_find_internal)
 *	the status of the transaction.  A txnid of 0 means the record
 *	was generated while not in a transaction.
 *
 * PUBLIC: int __db_txnlist_find __P((ENV *,
 * PUBLIC:     DB_TXNHEAD *, u_int32_t, u_int32_t *));
 */
int
__db_txnlist_find(env, hp, txnid, statusp)
	ENV *env;
	DB_TXNHEAD *hp;
	u_int32_t txnid, *statusp;
{
	DB_TXNLIST *entry;

	if (txnid == 0)
		return (DB_NOTFOUND);

	return (__db_txnlist_find_internal(env, hp,
	    TXNLIST_TXNID, txnid, &entry, 0, statusp));
}

/*
 * __db_txnlist_update --
 *	Change the status of an existing transaction entry.
 *	Returns DB_NOTFOUND if no such entry exists.
 *
 * PUBLIC: int __db_txnlist_update __P((ENV *, DB_TXNHEAD *,
 * PUBLIC:     u_int32_t, u_int32_t, DB_LSN *, u_int32_t *, int));
 */
int
__db_txnlist_update(env, hp, txnid, status, lsn, ret_status, add_ok)
	ENV *env;
	DB_TXNHEAD *hp;
	u_int32_t txnid, status;
	DB_LSN *lsn;
	u_int32_t *ret_status;
	int add_ok;
{
	DB_TXNLIST *elp;
	int ret;

	if (txnid == 0)
		return (DB_NOTFOUND);

	ret = __db_txnlist_find_internal(env,
	    hp, TXNLIST_TXNID, txnid, &elp, 0, ret_status);

	if (ret == DB_NOTFOUND && add_ok) {
		*ret_status = status;
		return (__db_txnlist_add(env, hp, txnid, status, lsn));
	}
	if (ret != 0)
		return (ret);

	if (*ret_status == TXN_IGNORE)
		return (0);

	elp->u.t.status = status;

	if (lsn != NULL && IS_ZERO_LSN(hp->maxlsn) && status == TXN_COMMIT)
		hp->maxlsn = *lsn;

	return (ret);
}

/*
 * __db_txnlist_find_internal --
 *	Find an entry on the transaction list.  If the entry is not there or
 *	the list pointer is not initialized we return DB_NOTFOUND.  If the
 *	item is found, we return the status.  Currently we always call this
 *	with an initialized list pointer but checking for NULL keeps it general.
 */
static int
__db_txnlist_find_internal(env,
    hp, type, txnid, txnlistp, delete, statusp)
	ENV *env;
	DB_TXNHEAD *hp;
	db_txnlist_type type;
	u_int32_t  txnid;
	DB_TXNLIST **txnlistp;
	int delete;
	u_int32_t *statusp;
{
	struct __db_headlink *head;
	DB_TXNLIST *p;
	u_int32_t generation, hash;
	int ret;

	ret = 0;

	if (hp == NULL)
		return (DB_NOTFOUND);

	switch (type) {
	case TXNLIST_TXNID:
		hash = txnid;
		FIND_GENERATION(hp, txnid, generation);
		break;
	case TXNLIST_DELETE:
	case TXNLIST_LSN:
	default:
		return (__env_panic(env, EINVAL));
	}

	head = &hp->head[DB_TXNLIST_MASK(hp, hash)];
	LIST_FOREACH(p, head, links) {
		if (p->type != type)
			continue;
		switch (type) {
		case TXNLIST_TXNID:
			if (p->u.t.txnid != txnid ||
			    generation != p->u.t.generation)
				continue;
			*statusp = p->u.t.status;
			break;

		case TXNLIST_DELETE:
		case TXNLIST_LSN:
		default:
			return (__env_panic(env, EINVAL));
		}
		if (delete == 1) {
			LIST_REMOVE(p, links);
			__os_free(env, p);
			*txnlistp = NULL;
		} else if (p != LIST_FIRST(head)) {
			/* Move it to head of list. */
			LIST_REMOVE(p, links);
			LIST_INSERT_HEAD(head, p, links);
			*txnlistp = p;
		} else
			*txnlistp = p;
		return (ret);
	}

	return (DB_NOTFOUND);
}

/*
 * __db_txnlist_gen --
 *	Change the current generation number.
 *
 * PUBLIC: int __db_txnlist_gen __P((ENV *,
 * PUBLIC:       DB_TXNHEAD *, int, u_int32_t, u_int32_t));
 */
int
__db_txnlist_gen(env, hp, incr, min, max)
	ENV *env;
	DB_TXNHEAD *hp;
	int incr;
	u_int32_t min, max;
{
	int ret;

	/*
	 * During recovery generation numbers keep track of "restart"
	 * checkpoints and recycle records.  Restart checkpoints occur
	 * whenever we take a checkpoint and there are no outstanding
	 * transactions.  When that happens, we can reset transaction IDs
	 * back to TXNID_MINIMUM.  Currently we only do the reset
	 * at then end of recovery.  Recycle records occur when txnids
	 * are exhausted during runtime.  A free range of ids is identified
	 * and logged.  This code maintains a stack of ranges.  A txnid
	 * is given the generation number of the first range it falls into
	 * in the stack.
	 */
	if (incr < 0) {
		--hp->generation;
		memmove(hp->gen_array, &hp->gen_array[1],
		    (hp->generation + 1) * sizeof(hp->gen_array[0]));
	} else {
		++hp->generation;
		if (hp->generation >= hp->gen_alloc) {
			hp->gen_alloc *= 2;
			if ((ret = __os_realloc(env, hp->gen_alloc *
			    sizeof(hp->gen_array[0]), &hp->gen_array)) != 0)
				return (ret);
		}
		memmove(&hp->gen_array[1], &hp->gen_array[0],
		    hp->generation * sizeof(hp->gen_array[0]));
		hp->gen_array[0].generation = hp->generation;
		hp->gen_array[0].txn_min = min;
		hp->gen_array[0].txn_max = max;
	}
	return (0);
}

/*
 * __db_txnlist_lsnadd --
 *	Save the prev_lsn from a txn_child record.
 *
 * PUBLIC: int __db_txnlist_lsnadd __P((ENV *, DB_TXNHEAD *, DB_LSN *));
 */
int
__db_txnlist_lsnadd(env, hp, lsnp)
	ENV *env;
	DB_TXNHEAD *hp;
	DB_LSN *lsnp;
{
	DB_TXNLIST *elp;
	int ret;

	if (IS_ZERO_LSN(*lsnp))
		return (0);

	LIST_FOREACH(elp, &hp->head[0], links)
		if (elp->type == TXNLIST_LSN)
			break;

	if (elp == NULL) {
		if ((ret = __db_txnlist_lsninit(env, hp, lsnp)) != 0)
			return (ret);
		return (DB_SURPRISE_KID);
	}

	if (elp->u.l.stack_indx == elp->u.l.stack_size) {
		elp->u.l.stack_size <<= 1;
		if ((ret = __os_realloc(env, sizeof(DB_LSN) *
		     elp->u.l.stack_size, &elp->u.l.lsn_stack)) != 0) {
			__db_txnlist_end(env, hp);
			return (ret);
		}
	}
	elp->u.l.lsn_stack[elp->u.l.stack_indx++] = *lsnp;

	return (0);
}

/*
 * __db_txnlist_lsnget --
 *
 * PUBLIC: int __db_txnlist_lsnget __P((ENV *,
 * PUBLIC:     DB_TXNHEAD *, DB_LSN *, u_int32_t));
 *	Get the lsn saved from a txn_child record.
 */
int
__db_txnlist_lsnget(env, hp, lsnp, flags)
	ENV *env;
	DB_TXNHEAD *hp;
	DB_LSN *lsnp;
	u_int32_t flags;
{
	DB_TXNLIST *elp;

	COMPQUIET(env, NULL);
	COMPQUIET(flags, 0);

	LIST_FOREACH(elp, &hp->head[0], links)
		if (elp->type == TXNLIST_LSN)
			break;

	if (elp == NULL || elp->u.l.stack_indx == 0) {
		ZERO_LSN(*lsnp);
		return (0);
	}

	*lsnp = elp->u.l.lsn_stack[--elp->u.l.stack_indx];

	return (0);
}

/*
 * __db_txnlist_lsninit --
 *	Initialize a transaction list with an lsn array entry.
 *
 * PUBLIC: int __db_txnlist_lsninit __P((ENV *, DB_TXNHEAD *, DB_LSN *));
 */
int
__db_txnlist_lsninit(env, hp, lsnp)
	ENV *env;
	DB_TXNHEAD *hp;
	DB_LSN *lsnp;
{
	DB_TXNLIST *elp;
	int ret;

	elp = NULL;

	if ((ret = __os_malloc(env, sizeof(DB_TXNLIST), &elp)) != 0)
		goto err;
	LIST_INSERT_HEAD(&hp->head[0], elp, links);

	elp->type = TXNLIST_LSN;
	if ((ret = __os_malloc(env,
	    sizeof(DB_LSN) * DB_LSN_STACK_SIZE, &elp->u.l.lsn_stack)) != 0)
		goto err;
	elp->u.l.stack_indx = 1;
	elp->u.l.stack_size = DB_LSN_STACK_SIZE;
	elp->u.l.lsn_stack[0] = *lsnp;

	return (0);

err:	__db_txnlist_end(env, hp);
	return (ret);
}

#ifdef DEBUG
/*
 * __db_txnlist_print --
 *	Print out the transaction list.
 *
 * PUBLIC: void __db_txnlist_print __P((DB_TXNHEAD *));
 */
void
__db_txnlist_print(hp)
	DB_TXNHEAD *hp;
{
	DB_TXNLIST *p;
	u_int32_t i;
	char *txntype;

	printf("Maxid: %lu Generation: %lu\n",
	    (u_long)hp->maxid, (u_long)hp->generation);
	for (i = 0; i < hp->nslots; i++)
		LIST_FOREACH(p, &hp->head[i], links) {
			if (p->type != TXNLIST_TXNID) {
				printf("Unrecognized type: %d\n", p->type);
				continue;
			}
			switch (p->u.t.status) {
			case TXN_OK:
				txntype = "OK";
				break;
			case TXN_COMMIT:
				txntype = "commit";
				break;
			case TXN_PREPARE:
				txntype = "prepare";
				break;
			case TXN_ABORT:
				txntype = "abort";
				break;
			case TXN_IGNORE:
				txntype = "ignore";
				break;
			case TXN_EXPECTED:
				txntype = "expected";
				break;
			case TXN_UNEXPECTED:
				txntype = "unexpected";
				break;
			default:
				txntype = "UNKNOWN";
				break;
			}
			printf("TXNID: %lx(%lu): %s\n",
			    (u_long)p->u.t.txnid,
			    (u_long)p->u.t.generation, txntype);
		}
}
#endif