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txn.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998, 1999, 2000
 *    Sleepycat Software.  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.
 */

#include "db_config.h"

#ifndef lint
static const char revid[] = "$Id: txn.c,v 11.61 2001/01/10 18:18:52 bostic Exp $";
#endif /* not lint */

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

#if TIME_WITH_SYS_TIME
#include <sys/time.h>
#include <time.h>
#else
#if HAVE_SYS_TIME_H
#include <sys/time.h>
#else
#include <time.h>
#endif
#endif

#include <string.h>
#endif

#ifdef  HAVE_RPC
#include "db_server.h"
#endif

#include "db_int.h"
#include "db_shash.h"
#include "txn.h"
#include "lock.h"
#include "log.h"
#include "db_dispatch.h"
#include "db_page.h"
#include "db_ext.h"

#ifdef HAVE_RPC
#include "gen_client_ext.h"
#include "rpc_client_ext.h"
#endif

static int  __txn_begin __P((DB_TXN *));
static int  __txn_isvalid __P((const DB_TXN *, TXN_DETAIL **, u_int32_t));
static int  __txn_undo __P((DB_TXN *));

/*
 * txn_begin --
 *    This is a wrapper to the actual begin process.  Normal txn_begin()
 * allocates a DB_TXN structure for the caller, while txn_xa_begin() does
 * not.  Other than that, both call into the common __txn_begin code().
 *
 * Internally, we use TXN_DETAIL structures, but the DB_TXN structure
 * provides access to the transaction ID and the offset in the transaction
 * region of the TXN_DETAIL structure.
 */
int
txn_begin(dbenv, parent, txnpp, flags)
      DB_ENV *dbenv;
      DB_TXN *parent, **txnpp;
      u_int32_t flags;
{
      DB_TXN *txn;
      int ret;

#ifdef HAVE_RPC
      if (F_ISSET(dbenv, DB_ENV_RPCCLIENT))
            return (__dbcl_txn_begin(dbenv, parent, txnpp, flags));
#endif

      PANIC_CHECK(dbenv);
      ENV_REQUIRES_CONFIG(dbenv, dbenv->tx_handle, DB_INIT_TXN);

      if ((ret = __db_fchk(dbenv,
          "txn_begin", flags,
          DB_TXN_NOWAIT | DB_TXN_NOSYNC | DB_TXN_SYNC)) != 0)
            return (ret);
      if ((ret = __db_fcchk(dbenv,
          "txn_begin", flags, DB_TXN_NOSYNC, DB_TXN_SYNC)) != 0)
            return (ret);

      if ((ret = __os_calloc(dbenv, 1, sizeof(DB_TXN), &txn)) != 0)
            return (ret);

      txn->mgrp = dbenv->tx_handle;
      txn->parent = parent;
      TAILQ_INIT(&txn->kids);
      txn->flags = TXN_MALLOC;
      if (LF_ISSET(DB_TXN_NOSYNC))
            F_SET(txn, TXN_NOSYNC);
      if (LF_ISSET(DB_TXN_SYNC))
            F_SET(txn, TXN_SYNC);
      if (LF_ISSET(DB_TXN_NOWAIT))
            F_SET(txn, TXN_NOWAIT);

      if ((ret = __txn_begin(txn)) != 0) {
            __os_free(txn, sizeof(DB_TXN));
            txn = NULL;
      }

      if (txn != NULL && parent != NULL)
            TAILQ_INSERT_HEAD(&parent->kids, txn, klinks);

      *txnpp = txn;
      return (ret);
}

/*
 * __txn_xa_begin --
 *    XA version of txn_begin.
 *
 * PUBLIC: int __txn_xa_begin __P((DB_ENV *, DB_TXN *));
 */
int
__txn_xa_begin(dbenv, txn)
      DB_ENV *dbenv;
      DB_TXN *txn;
{
      PANIC_CHECK(dbenv);

      memset(txn, 0, sizeof(DB_TXN));

      txn->mgrp = dbenv->tx_handle;

      return (__txn_begin(txn));
}

/*
 * __txn_begin --
 *    Normal DB version of txn_begin.
 */
static int
__txn_begin(txn)
      DB_TXN *txn;
{
      DB_ENV *dbenv;
      DB_LSN begin_lsn;
      DB_TXNMGR *mgr;
      DB_TXNREGION *region;
      TXN_DETAIL *td;
      size_t off;
      u_int32_t id;
      int ret;

      mgr = txn->mgrp;
      dbenv = mgr->dbenv;
      region = mgr->reginfo.primary;

      /*
       * We do not have to write begin records (and if we do not, then we
       * need never write records for read-only transactions).  However,
       * we do need to find the current LSN so that we can store it in the
       * transaction structure, so we can know where to take checkpoints.
       */
      if (LOGGING_ON(dbenv) &&
          (ret = log_put(dbenv, &begin_lsn, NULL, DB_CURLSN)) != 0)
            goto err2;

      R_LOCK(dbenv, &mgr->reginfo);

      /* Make sure that last_txnid is not going to wrap around. */
      if (region->last_txnid == TXN_INVALID) {
            __db_err(dbenv,
"txn_begin: transaction ID wrapped.  Exit the database environment\nand restart the application as if application failure had occurred");
            ret = EINVAL;
            goto err1;
      }

      /* Allocate a new transaction detail structure. */
      if ((ret =
          __db_shalloc(mgr->reginfo.addr, sizeof(TXN_DETAIL), 0, &td)) != 0) {
            __db_err(dbenv,
                 "Unable to allocate memory for transaction detail");
            goto err1;
      }

      /* Place transaction on active transaction list. */
      SH_TAILQ_INSERT_HEAD(&region->active_txn, td, links, __txn_detail);

      id = ++region->last_txnid;
      ++region->nbegins;
      if (++region->nactive > region->maxnactive)
            region->maxnactive = region->nactive;

      td->txnid = id;
      td->begin_lsn = begin_lsn;
      ZERO_LSN(td->last_lsn);
      td->status = TXN_RUNNING;
      if (txn->parent != NULL)
            td->parent = txn->parent->off;
      else
            td->parent = INVALID_ROFF;

      off = R_OFFSET(&mgr->reginfo, td);
      R_UNLOCK(dbenv, &mgr->reginfo);

      ZERO_LSN(txn->last_lsn);
      txn->txnid = id;
      txn->off = off;

      /*
       * If this is a transaction family, we must link the child to the
       * maximal grandparent in the lock table for deadlock detection.
       */
      if (txn->parent != NULL && LOCKING_ON(dbenv))
            if ((ret = __lock_addfamilylocker(dbenv,
                txn->parent->txnid, txn->txnid)) != 0)
                  goto err2;

      if (F_ISSET(txn, TXN_MALLOC)) {
            MUTEX_THREAD_LOCK(dbenv, mgr->mutexp);
            TAILQ_INSERT_TAIL(&mgr->txn_chain, txn, links);
            MUTEX_THREAD_UNLOCK(dbenv, mgr->mutexp);
      }

      return (0);

err1: R_UNLOCK(dbenv, &mgr->reginfo);

err2: return (ret);
}

/*
 * txn_commit --
 *    Commit a transaction.
 */
int
txn_commit(txnp, flags)
      DB_TXN *txnp;
      u_int32_t flags;
{
      DB_ENV *dbenv;
      DB_TXN *kid;
      int is_commit, ret, t_ret;

      dbenv = txnp->mgrp->dbenv;

#ifdef HAVE_RPC
      if (F_ISSET(dbenv, DB_ENV_RPCCLIENT))
            return (__dbcl_txn_commit(txnp, flags));
#endif

      PANIC_CHECK(dbenv);

      if ((ret = __txn_isvalid(txnp, NULL, TXN_COMMITTED)) != 0)
            return (ret);

      /*
       * We clear flags that are incorrect, ignoring any flag errors, and
       * default to synchronous operations.  By definition, transaction
       * handles are dead when we return, and this error should never
       * happen, but we don't want to fail in the field 'cause the app is
       * specifying the wrong flag for some reason.
       */
      if (__db_fchk(dbenv,
          "txn_commit", flags, DB_TXN_NOSYNC | DB_TXN_SYNC) != 0)
            flags = DB_TXN_SYNC;
      if (__db_fcchk(dbenv,
          "txn_commit", flags, DB_TXN_NOSYNC, DB_TXN_SYNC) != 0)
            flags = DB_TXN_SYNC;
      if (LF_ISSET(DB_TXN_NOSYNC)) {
            F_CLR(txnp, TXN_SYNC);
            F_SET(txnp, TXN_NOSYNC);
      }
      if (LF_ISSET(DB_TXN_SYNC)) {
            F_CLR(txnp, TXN_NOSYNC);
            F_SET(txnp, TXN_SYNC);
      }

      /*
       * Commit any unresolved children.  If there's an error, abort any
       * unresolved children and the parent.
       */
      while ((kid = TAILQ_FIRST(&txnp->kids)) != NULL)
            if ((ret = txn_commit(kid, flags)) != 0) {
                  while ((kid = TAILQ_FIRST(&txnp->kids)) != NULL)
                        (void)txn_abort(kid);
                  (void)txn_abort(txnp);
                  goto err;
            }

      /*
       * If there are any log records, write a log record and sync the log,
       * else do no log writes.  If the commit is for a child transaction,
       * we do not need to commit the child synchronously since it may still
       * abort (if its parent aborts), and otherwise its parent or ultimate
       * ancestor will write synchronously.
       *
       * I'd rather return a logging error than a flag-wrong error, so if
       * the log routines fail, set "ret" without regard to previous value.
       */
      if (LOGGING_ON(dbenv) && !IS_ZERO_LSN(txnp->last_lsn)) {
            if (txnp->parent == NULL) {
                  if ((t_ret = __txn_regop_log(dbenv,
                      txnp, &txnp->last_lsn,
                      (F_ISSET(dbenv, DB_ENV_TXN_NOSYNC) &&
                      !F_ISSET(txnp, TXN_SYNC)) ||
                      F_ISSET(txnp, TXN_NOSYNC) ?  0 : DB_FLUSH,
                      TXN_COMMIT, (int32_t)time(NULL))) != 0) {
                        ret = t_ret;
                        goto err;
                  }
            } else {
                  /* Log the commit in the parent! */
                  if ((t_ret = __txn_child_log(dbenv,
                      txnp->parent, &txnp->parent->last_lsn,
                      0, txnp->txnid, &txnp->last_lsn)) != 0) {
                        ret = t_ret;
                        goto err;
                  }

                  F_SET(txnp->parent, TXN_CHILDCOMMIT);
            }
      }

      is_commit = 1;
      if (0) {
err:        is_commit = 0;
      }
      if ((t_ret = __txn_end(txnp, is_commit)) != 0 && ret == 0)
            ret = t_ret;
      return (ret);
}

/*
 * txn_abort --
 *    Abort a transaction.
 */
int
txn_abort(txnp)
      DB_TXN *txnp;
{
      DB_ENV *dbenv;
      DB_TXN *kid;
      int ret, t_ret;

      dbenv = txnp->mgrp->dbenv;

#ifdef HAVE_RPC
      if (F_ISSET(dbenv, DB_ENV_RPCCLIENT))
            return (__dbcl_txn_abort(txnp));
#endif

      PANIC_CHECK(dbenv);

      if ((ret = __txn_isvalid(txnp, NULL, TXN_ABORTED)) != 0)
            return (ret);

      /* Abort any unresolved children. */
      while ((kid = TAILQ_FIRST(&txnp->kids)) != NULL)
            if ((t_ret = txn_abort(kid)) != 0 && ret == 0)
                  ret = t_ret;

      if ((t_ret = __txn_undo(txnp)) != 0 && ret == 0)
            ret = t_ret;

      if ((t_ret = __txn_end(txnp, 0)) != 0 && ret == 0)
            ret = t_ret;
      return (ret);
}

/*
 * txn_prepare --
 *    Flush the log so a future commit is guaranteed to succeed.
 */
int
txn_prepare(txnp)
      DB_TXN *txnp;
{
      DBT xid;
      DB_ENV *dbenv;
      DB_TXN *kid;
      TXN_DETAIL *td;
      int ret;

      dbenv = txnp->mgrp->dbenv;

#ifdef HAVE_RPC
      if (F_ISSET(dbenv, DB_ENV_RPCCLIENT))
            return (__dbcl_txn_prepare(txnp));
#endif

      PANIC_CHECK(dbenv);

      if ((ret = __txn_isvalid(txnp, &td, TXN_PREPARED)) != 0)
            return (ret);

      /* Prepare any unresolved children. */
      while ((kid = TAILQ_FIRST(&txnp->kids)) != NULL)
            if ((ret = txn_prepare(kid)) != 0)
                  return (ret);

      /*
       * We indicate that a transaction is an XA transaction by putting
       * a valid size in the xid.size fiels.  XA requires that the transaction
       * be either ENDED or SUSPENDED when prepare is called, so we know
       * that if the xa_status isn't in one of those states, but we are
       * calling prepare that we are not an XA transaction.
       */

      if (LOGGING_ON(dbenv)) {
            memset(&xid, 0, sizeof(xid));
            xid.data = td->xid;
            xid.size = td->xa_status != TXN_XA_ENDED &&
                td->xa_status != TXN_XA_SUSPENDED ?  0 : sizeof(td->xid);
            if ((ret = __txn_xa_regop_log(dbenv, txnp, &txnp->last_lsn,
                (F_ISSET(dbenv, DB_ENV_TXN_NOSYNC) &&
                !F_ISSET(txnp, TXN_SYNC)) ||
                F_ISSET(txnp, TXN_NOSYNC) ? 0 : DB_FLUSH, TXN_PREPARE,
                &xid, td->format, td->gtrid, td->bqual,
                &td->begin_lsn)) != 0) {
                  __db_err(dbenv, "txn_prepare: log_write failed %s",
                      db_strerror(ret));
                  return (ret);
            }
            if (txnp->parent != NULL)
                  F_SET(txnp->parent, TXN_CHILDCOMMIT);
      }

      MUTEX_THREAD_LOCK(dbenv, txnp->mgrp->mutexp);
      td->status = TXN_PREPARED;
      MUTEX_THREAD_UNLOCK(dbenv, txnp->mgrp->mutexp);
      return (0);
}

/*
 * txn_id --
 *    Return the transaction ID.
 */
u_int32_t
txn_id(txnp)
      DB_TXN *txnp;
{
      return (txnp->txnid);
}

/*
 * __txn_isvalid --
 *    Return 0 if the txnp is reasonable, otherwise panic.
 */
static int
__txn_isvalid(txnp, tdp, op)
      const DB_TXN *txnp;
      TXN_DETAIL **tdp;
      u_int32_t op;
{
      DB_TXNMGR *mgrp;
      TXN_DETAIL *tp;

      mgrp = txnp->mgrp;

      /* Check for live cursors. */
      if (txnp->cursors != 0) {
            __db_err(mgrp->dbenv, "transaction has active cursors");
            goto err;
      }

      /* Check transaction's status. */
      tp = (TXN_DETAIL *)R_ADDR(&mgrp->reginfo, txnp->off);
      if (tdp != NULL)
            *tdp = tp;

      switch (tp->status) {
      case TXN_ABORTED:
      case TXN_COMMITTED:
      default:
            __db_err(mgrp->dbenv, "transaction already %s",
                tp->status == TXN_COMMITTED ? "committed" : "aborted");
            goto err;
      case TXN_PREPARED:
            if (op == TXN_PREPARED) {
                  __db_err(mgrp->dbenv, "transaction already prepared");
                  goto err;
            }
      case TXN_RUNNING:
            break;
      }

      return (0);

err:  /*
       * If there's a serious problem with the transaction, panic.  TXN
       * handles are dead by definition when we return, and if you use
       * a cursor you forgot to close, we have no idea what will happen.
       */
      return (__db_panic(mgrp->dbenv, EINVAL));
}

/*
 * __txn_end --
 *    Internal transaction end routine.
 *
 * PUBLIC: int __txn_end __P((DB_TXN *, int));
 */
int
__txn_end(txnp, is_commit)
      DB_TXN *txnp;
      int is_commit;
{
      DB_ENV *dbenv;
      DB_LOCKREQ request;
      DB_TXNMGR *mgr;
      DB_TXNREGION *region;
      TXN_DETAIL *tp;
      int ret;

      mgr = txnp->mgrp;
      dbenv = mgr->dbenv;
      region = mgr->reginfo.primary;

      /* Release the locks. */
      request.op = txnp->parent == NULL ||
          is_commit == 0 ? DB_LOCK_PUT_ALL : DB_LOCK_INHERIT;

      if (LOCKING_ON(dbenv)) {
            ret = lock_vec(dbenv, txnp->txnid, 0, &request, 1, NULL);
            if (ret != 0 && (ret != DB_LOCK_DEADLOCK || is_commit)) {
                  __db_err(dbenv, "%s: release locks failed %s",
                      is_commit ? "txn_commit" : "txn_abort",
                      db_strerror(ret));
                  __db_panic(dbenv, ret);
            }
      }

      /* End the transaction. */
      R_LOCK(dbenv, &mgr->reginfo);

      tp = (TXN_DETAIL *)R_ADDR(&mgr->reginfo, txnp->off);
      SH_TAILQ_REMOVE(&region->active_txn, tp, links, __txn_detail);
      __db_shalloc_free(mgr->reginfo.addr, tp);

      if (is_commit)
            region->ncommits++;
      else
            region->naborts++;
      --region->nactive;

      R_UNLOCK(dbenv, &mgr->reginfo);

      /*
       * The transaction cannot get more locks, remove its locker info.
       */
      if (LOCKING_ON(dbenv))
            __lock_freefamilylocker(dbenv->lk_handle, txnp->txnid);
      if (txnp->parent != NULL)
            TAILQ_REMOVE(&txnp->parent->kids, txnp, klinks);

      /* Free the space. */
      if (F_ISSET(txnp, TXN_MALLOC)) {
            MUTEX_THREAD_LOCK(dbenv, mgr->mutexp);
            TAILQ_REMOVE(&mgr->txn_chain, txnp, links);
            MUTEX_THREAD_UNLOCK(dbenv, mgr->mutexp);

            __os_free(txnp, sizeof(*txnp));
      }

      return (0);
}

/*
 * __txn_undo --
 *    Undo the transaction with id txnid.  Returns 0 on success and
 *    errno on failure.
 */
static int
__txn_undo(txnp)
      DB_TXN *txnp;
{
      DBT rdbt;
      DB_ENV *dbenv;
      DB_LSN key_lsn;
      DB_TXNMGR *mgr;
      void *txnlist;
      int ret, threaded;

      mgr = txnp->mgrp;
      dbenv = mgr->dbenv;
      txnlist = NULL;

      if (!LOGGING_ON(dbenv))
            return (0);

      /*
       * This is the simplest way to code this, but if the mallocs during
       * recovery turn out to be a performance issue, we can do the
       * allocation here and use DB_DBT_USERMEM.
       */
      memset(&rdbt, 0, sizeof(rdbt));
      threaded = F_ISSET(dbenv, DB_ENV_THREAD) ? 1 : 0;
      if (threaded)
            F_SET(&rdbt, DB_DBT_MALLOC);

      key_lsn = txnp->last_lsn;

      /* Allocate a transaction list for children or aborted page creates. */
      if ((ret = __db_txnlist_init(dbenv, &txnlist)) != 0)
            return (ret);

      if (F_ISSET(txnp, TXN_CHILDCOMMIT) &&
          (ret = __db_txnlist_lsninit(dbenv,
          txnlist, &txnp->last_lsn)) != 0)
            return (ret);

      for (ret = 0; ret == 0 && !IS_ZERO_LSN(key_lsn);) {
            /*
             * The dispatch routine returns the lsn of the record
             * before the current one in the key_lsn argument.
             */
            if ((ret = log_get(dbenv, &key_lsn, &rdbt, DB_SET)) == 0) {
                  ret = __db_dispatch(dbenv,
                      &rdbt, &key_lsn, DB_TXN_ABORT, txnlist);
                  if (threaded && rdbt.data != NULL) {
                        __os_free(rdbt.data, rdbt.size);
                        rdbt.data = NULL;
                  }
                  if (F_ISSET(txnp, TXN_CHILDCOMMIT))
                        (void)__db_txnlist_lsnadd(dbenv,
                            txnlist, &key_lsn, 0);
            }
            if (ret != 0) {
                  __db_err(txnp->mgrp->dbenv,
                      "txn_abort: Log undo failed for LSN: %lu %lu: %s",
                      (u_long)key_lsn.file, (u_long)key_lsn.offset,
                      db_strerror(ret));
                  if (txnlist != NULL)
                        __db_txnlist_end(dbenv, txnlist);
                  return (ret);
            }
      }

      if (txnlist != NULL) {
            __db_do_the_limbo(dbenv, txnlist);
            __db_txnlist_end(dbenv, txnlist);
      }

      return (ret);
}

/*
 * Transaction checkpoint.
 * If either kbytes or minutes is non-zero, then we only take the checkpoint
 * more than "minutes" minutes have passed since the last checkpoint or if
 * more than "kbytes" of log data have been written since the last checkpoint.
 * When taking a checkpoint, find the oldest active transaction and figure out
 * its first LSN.  This is the lowest LSN we can checkpoint, since any record
 * written after since that point may be involved in a transaction and may
 * therefore need to be undone in the case of an abort.
 */
int
txn_checkpoint(dbenv, kbytes, minutes, flags)
      DB_ENV *dbenv;
      u_int32_t kbytes, minutes, flags;
{
      DB_LOG *dblp;
      DB_LSN ckp_lsn, sync_lsn, last_ckp;
      DB_TXNMGR *mgr;
      DB_TXNREGION *region;
      LOG *lp;
      TXN_DETAIL *txnp;
      time_t last_ckp_time, now;
      u_int32_t bytes, mbytes;
      int interval, ret;

#ifdef HAVE_RPC
      if (F_ISSET(dbenv, DB_ENV_RPCCLIENT))
            return (__dbcl_txn_checkpoint(dbenv, kbytes, minutes));
#endif
      PANIC_CHECK(dbenv);
      ENV_REQUIRES_CONFIG(dbenv, dbenv->tx_handle, DB_INIT_TXN);

      mgr = dbenv->tx_handle;
      region = mgr->reginfo.primary;
      dblp = dbenv->lg_handle;
      lp = dblp->reginfo.primary;

      /*
       * Check if we need to checkpoint.
       */
      ZERO_LSN(ckp_lsn);

      if (LF_ISSET(DB_FORCE))
            goto do_ckp;

      R_LOCK(dbenv, &dblp->reginfo);
      mbytes = lp->stat.st_wc_mbytes;
      /*
       * We add the current buffer offset so as to count bytes that
       * have not yet been written, but are sitting in the log buffer.
       */
      bytes = lp->stat.st_wc_bytes + lp->b_off;
      ckp_lsn = lp->lsn;
      R_UNLOCK(dbenv, &dblp->reginfo);

      /* Don't checkpoint a quiescent database. */
      if (bytes == 0 && mbytes == 0)
            return (0);

      if (kbytes != 0 && mbytes * 1024 + bytes / 1024 >= (u_int32_t)kbytes)
            goto do_ckp;

      if (minutes != 0) {
            (void)time(&now);

            R_LOCK(dbenv, &mgr->reginfo);
            last_ckp_time = region->time_ckp;
            R_UNLOCK(dbenv, &mgr->reginfo);

            if (now - last_ckp_time >= (time_t)(minutes * 60))
                  goto do_ckp;
      }

      /*
       * If we checked time and data and didn't go to checkpoint,
       * we're done.
       */
      if (minutes != 0 || kbytes != 0)
            return (0);

do_ckp:
      if (IS_ZERO_LSN(ckp_lsn)) {
            R_LOCK(dbenv, &dblp->reginfo);
            ckp_lsn = lp->lsn;
            R_UNLOCK(dbenv, &dblp->reginfo);
      }

      /*
       * We have to find an LSN such that all transactions begun
       * before that LSN are complete.
       */
      R_LOCK(dbenv, &mgr->reginfo);

      if (IS_ZERO_LSN(region->pending_ckp)) {
            for (txnp =
                SH_TAILQ_FIRST(&region->active_txn, __txn_detail);
                txnp != NULL;
                txnp = SH_TAILQ_NEXT(txnp, links, __txn_detail)) {

                  /*
                   * Look through the active transactions for the
                   * lowest begin lsn.
                   */
                  if (!IS_ZERO_LSN(txnp->begin_lsn) &&
                      log_compare(&txnp->begin_lsn, &ckp_lsn) < 0)
                        ckp_lsn = txnp->begin_lsn;
            }
            region->pending_ckp = ckp_lsn;
      } else
            ckp_lsn = region->pending_ckp;

      R_UNLOCK(dbenv, &mgr->reginfo);

      /*
       * Try three times to sync the mpool buffers up to the specified LSN,
       * sleeping 1, 2 and 4 seconds between attempts.
       */
      if (MPOOL_ON(dbenv))
            for (interval = 1;;) {
                  /*
                   * memp_sync may change the lsn you pass it, so don't
                   * pass it the actual ckp_lsn, pass it a local instead.
                   */
                  sync_lsn = ckp_lsn;
                  if ((ret = memp_sync(dbenv, &sync_lsn)) == 0)
                        break;

                  /*
                   * ret == DB_INCOMPLETE means there are still buffers
                   * to flush, the checkpoint is not complete.
                   */
                  if (ret == DB_INCOMPLETE) {
                        if (interval > 4)
                              return (ret);

                        (void)__os_sleep(dbenv, interval, 0);
                        interval *= 2;
                  } else {
                        __db_err(dbenv,
                            "txn_checkpoint: failure in memp_sync %s",
                            db_strerror(ret));
                        return (ret);
                  }
            }

      if (LOGGING_ON(dbenv)) {
            R_LOCK(dbenv, &mgr->reginfo);
            last_ckp = region->last_ckp;
            ZERO_LSN(region->pending_ckp);
            R_UNLOCK(dbenv, &mgr->reginfo);

            if ((ret = __txn_ckp_log(dbenv,
                NULL, &ckp_lsn, DB_CHECKPOINT, &ckp_lsn,
                &last_ckp, (int32_t)time(NULL))) != 0) {
                  __db_err(dbenv,
                      "txn_checkpoint: log failed at LSN [%ld %ld] %s",
                      (long)ckp_lsn.file, (long)ckp_lsn.offset,
                      db_strerror(ret));
                  return (ret);
            }

            R_LOCK(dbenv, &mgr->reginfo);
            region->last_ckp = ckp_lsn;
            (void)time(&region->time_ckp);
            R_UNLOCK(dbenv, &mgr->reginfo);
      }
      return (0);
}

/*
 * __txn_activekids --
 *    Return if this transaction has any active children.
 *
 * PUBLIC: int __txn_activekids __P((DB_ENV *, u_int32_t, DB_TXN *));
 */
int
__txn_activekids(dbenv, rectype, txnp)
      DB_ENV *dbenv;
      u_int32_t rectype;
      DB_TXN *txnp;
{
      /*
       * On a child commit, we know that there are children (i.e., the
       * commiting child at the least.  In that case, skip this check.
       */
      if (rectype == DB_txn_child)
            return (0);

      if (TAILQ_FIRST(&txnp->kids) != NULL) {
            __db_err(dbenv, "Child transaction is active");
            return (EPERM);
      }
      return (0);
}

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