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Overview
Comment:Experiment with using an atomic CPU primitive instead of a mutex for intra-process locking with the unix-excl VFS.
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Timelines: family | ancestors | descendants | both | mutexfree-shmlock
Files: files | file ages | folders
SHA3-256: 8f4cb9dd3396bcaaf85dcdb4e3ae3c96f28a4d71d72665c4abf7c221370be626
User & Date: dan 2018-12-06 18:58:58
Context
2018-12-10
09:45
Avoid a mutex in-and-out in unixShmBarrier() on this branch. Use __sync_synchronize() instead. check-in: a8c5fd86 user: dan tags: mutexfree-shmlock
2018-12-06
20:26
Add the mutexfree-shmlock experiment to the begin-concurrent-pnu branch. check-in: 3aead209 user: dan tags: begin-concurrent-pnu-mutexfree-shmlock
18:58
Experiment with using an atomic CPU primitive instead of a mutex for intra-process locking with the unix-excl VFS. check-in: 8f4cb9dd user: dan tags: mutexfree-shmlock
03:59
Invoking the sqlite3_trace() or sqlite3_trace_v2() interfaces cancels any sqlite3_profile() that is running. check-in: ec63d350 user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/os_unix.c.

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**   *  Locking primitives for the proxy uber-locking-method. (MacOSX only)
**   *  Definitions of sqlite3_vfs objects for all locking methods
**      plus implementations of sqlite3_os_init() and sqlite3_os_end().
*/
#include "sqliteInt.h"
#if SQLITE_OS_UNIX              /* This file is used on unix only */




/*
** There are various methods for file locking used for concurrency
** control:
**
**   1. POSIX locking (the default),
**   2. No locking,
**   3. Dot-file locking,
................................................................................
  int nRef;                  /* Number of unixShm objects pointing to this */
  unixShm *pFirst;           /* All unixShm objects pointing to this */
#ifdef SQLITE_DEBUG
  u8 exclMask;               /* Mask of exclusive locks held */
  u8 sharedMask;             /* Mask of shared locks held */
  u8 nextShmId;              /* Next available unixShm.id value */
#endif















};
















/*
** Structure used internally by this VFS to record the state of an
** open shared memory connection.
**
** The following fields are initialized when this object is created and
** are read-only thereafter:
................................................................................
       || flags==(SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE) );
  assert( n==1 || (flags & SQLITE_SHM_EXCLUSIVE)!=0 );
  assert( pShmNode->hShm>=0 || pDbFd->pInode->bProcessLock==1 );
  assert( pShmNode->hShm<0 || pDbFd->pInode->bProcessLock==0 );

  mask = (1<<(ofst+n)) - (1<<ofst);
  assert( n>1 || mask==(1<<ofst) );




















































  sqlite3_mutex_enter(pShmNode->pShmMutex);
  if( flags & SQLITE_SHM_UNLOCK ){
    u16 allMask = 0; /* Mask of locks held by siblings */

    /* See if any siblings hold this same lock */
    for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
      if( pX==p ) continue;







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**   *  Locking primitives for the proxy uber-locking-method. (MacOSX only)
**   *  Definitions of sqlite3_vfs objects for all locking methods
**      plus implementations of sqlite3_os_init() and sqlite3_os_end().
*/
#include "sqliteInt.h"
#if SQLITE_OS_UNIX              /* This file is used on unix only */

/* Turn this feature on in all builds for now */
#define SQLITE_MUTEXFREE_SHMLOCK 1

/*
** There are various methods for file locking used for concurrency
** control:
**
**   1. POSIX locking (the default),
**   2. No locking,
**   3. Dot-file locking,
................................................................................
  int nRef;                  /* Number of unixShm objects pointing to this */
  unixShm *pFirst;           /* All unixShm objects pointing to this */
#ifdef SQLITE_DEBUG
  u8 exclMask;               /* Mask of exclusive locks held */
  u8 sharedMask;             /* Mask of shared locks held */
  u8 nextShmId;              /* Next available unixShm.id value */
#endif

#ifdef SQLITE_MUTEXFREE_SHMLOCK
  /* In unix-excl mode, if SQLITE_MUTEXFREE_SHMLOCK is defined, all locks
  ** are stored in the following 64-bit value. There are in total 8 
  ** shm-locking slots, each of which are assigned 8-bits from the 64-bit
  ** value. The least-significant 8 bits correspond to shm-locking slot
  ** 0, and so on.
  **
  ** If the 8-bits corresponding to a shm-locking locking slot are set to
  ** 0xFF, then a write-lock is held on the slot. Or, if they are set to
  ** a non-zero value smaller than 0xFF, then they represent the total 
  ** number of read-locks held on the slot. There is no way to distinguish
  ** between a write-lock and 255 read-locks.  */
  u64 lockmask;
#endif
};

/*
** Atomic CAS primitive used in multi-process mode. Equivalent to:
** 
**   int unixCompareAndSwap(u32 *ptr, u32 oldval, u32 newval){
**     if( *ptr==oldval ){
**       *ptr = newval;
**       return 1;
**     }
**     return 0;
**   }
*/
#define unixCompareAndSwap(ptr,oldval,newval) \
    __sync_bool_compare_and_swap(ptr,oldval,newval)


/*
** Structure used internally by this VFS to record the state of an
** open shared memory connection.
**
** The following fields are initialized when this object is created and
** are read-only thereafter:
................................................................................
       || flags==(SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE) );
  assert( n==1 || (flags & SQLITE_SHM_EXCLUSIVE)!=0 );
  assert( pShmNode->hShm>=0 || pDbFd->pInode->bProcessLock==1 );
  assert( pShmNode->hShm<0 || pDbFd->pInode->bProcessLock==0 );

  mask = (1<<(ofst+n)) - (1<<ofst);
  assert( n>1 || mask==(1<<ofst) );

#ifdef SQLITE_MUTEXFREE_SHMLOCK
  if( pDbFd->pInode->bProcessLock ){

    while( 1 ){
      u64 lockmask = pShmNode->lockmask;
      u64 newmask = lockmask;
      int i;
      for(i=ofst; i<n+ofst; i++){
        int ix8 = i*8;
        u8 v = (lockmask >> (ix8)) & 0xFF;
        if( flags & SQLITE_SHM_UNLOCK ){
          if( flags & SQLITE_SHM_EXCLUSIVE ){
            if( p->exclMask & (1 << i) ){
              newmask = newmask & ~((u64)0xFF<<ix8);
            }
          }else{
            if( p->sharedMask & (1 << i) ){
              newmask = newmask & ~((u64)0xFF<<ix8) | ((u64)(v-1)<<ix8);
            }
          }
        }else{
          if( flags & SQLITE_SHM_EXCLUSIVE ){
            if( v ) return SQLITE_BUSY;
            if( (p->exclMask & (1 << i))==0 ){
              newmask = newmask | ((u64)0xFF<<ix8);
            }
          }else{
            if( v==0xFF ) return SQLITE_BUSY;
            if( (p->sharedMask & (1 << i))==0 ){
              newmask = newmask & ~((u64)0xFF<<ix8) | ((u64)(v+1)<<ix8);
            }
          }
        }
      }

      if( unixCompareAndSwap(&pShmNode->lockmask, lockmask, newmask) ) break;
    }

    if( flags & SQLITE_SHM_UNLOCK ){
      p->sharedMask &= ~mask;
      p->exclMask &= ~mask;
    }else if( flags & SQLITE_SHM_EXCLUSIVE ){
      p->exclMask |= mask;
    }else{
      p->sharedMask |= mask;
    }

    return SQLITE_OK;
  }
#endif

  sqlite3_mutex_enter(pShmNode->pShmMutex);
  if( flags & SQLITE_SHM_UNLOCK ){
    u16 allMask = 0; /* Mask of locks held by siblings */

    /* See if any siblings hold this same lock */
    for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
      if( pX==p ) continue;

Changes to src/test_vfs.c.

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  return TCL_OK;

 bad_args:
  Tcl_WrongNumArgs(interp, 1, objv, "VFSNAME ?-noshm BOOL? ?-fullshm BOOL? ?-default BOOL? ?-mxpathname INT? ?-szosfile INT? ?-iversion INT?");
  return TCL_ERROR;
}






















































int Sqlitetestvfs_Init(Tcl_Interp *interp){
  Tcl_CreateObjCommand(interp, "testvfs", testvfs_cmd, 0, 0);

  return TCL_OK;
}

#endif








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  return TCL_OK;

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  Tcl_WrongNumArgs(interp, 1, objv, "VFSNAME ?-noshm BOOL? ?-fullshm BOOL? ?-default BOOL? ?-mxpathname INT? ?-szosfile INT? ?-iversion INT?");
  return TCL_ERROR;
}

extern int getDbPointer(Tcl_Interp *interp, const char *zA, sqlite3 **ppDb);
extern const char *sqlite3ErrName(int);

/*
** tclcmd: vfs_shmlock DB DBNAME (shared|exclusive) (lock|unlock) OFFSET N
*/
static int SQLITE_TCLAPI test_vfs_shmlock(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  const char *azArg1[] = {"shared", "exclusive", 0};
  const char *azArg2[] = {"lock", "unlock", 0};
  sqlite3 *db = 0;
  int rc = SQLITE_OK;
  const char *zDbname = 0;
  int iArg1 = 0;
  int iArg2 = 0;
  int iOffset = 0;
  int n = 0;
  sqlite3_file *pFd;

  if( objc!=7 ){
    Tcl_WrongNumArgs(interp, 1, objv, 
        "DB DBNAME (shared|exclusive) (lock|unlock) OFFSET N"
    );
    return TCL_ERROR;
  }

  zDbname = Tcl_GetString(objv[2]);
  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) 
   || Tcl_GetIndexFromObj(interp, objv[3], azArg1, "ARG", 0, &iArg1) 
   || Tcl_GetIndexFromObj(interp, objv[4], azArg2, "ARG", 0, &iArg2) 
   || Tcl_GetIntFromObj(interp, objv[5], &iOffset)
   || Tcl_GetIntFromObj(interp, objv[6], &n)
  ){
    return TCL_ERROR;
  }

  sqlite3_file_control(db, zDbname, SQLITE_FCNTL_FILE_POINTER, (void*)&pFd);
  if( pFd==0 ){
    return TCL_ERROR;
  }
  rc = pFd->pMethods->xShmLock(pFd, iOffset, n, 
      (iArg1==0 ? SQLITE_SHM_SHARED : SQLITE_SHM_EXCLUSIVE)
    | (iArg2==0 ? SQLITE_SHM_LOCK : SQLITE_SHM_UNLOCK)
  );
  Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
  return TCL_OK;
}


int Sqlitetestvfs_Init(Tcl_Interp *interp){
  Tcl_CreateObjCommand(interp, "testvfs", testvfs_cmd, 0, 0);
  Tcl_CreateObjCommand(interp, "vfs_shmlock", test_vfs_shmlock, 0, 0);
  return TCL_OK;
}

#endif

Changes to test/lock_common.tcl.

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# This file contains code used by several different test scripts. The
# code in this file allows testfixture to control another process (or
# processes) to test locking.
#

proc do_multiclient_test {varname script} {

  foreach code [list {
    if {[info exists ::G(valgrind)]} { db close ; continue }
    set ::code2_chan [launch_testfixture]
    set ::code3_chan [launch_testfixture]
    proc code2 {tcl} { testfixture $::code2_chan $tcl }
    proc code3 {tcl} { testfixture $::code3_chan $tcl }
    set tn 1
  } {
    proc code2 {tcl} { uplevel #0 $tcl }
    proc code3 {tcl} { uplevel #0 $tcl }
    set tn 2
  }] {




    faultsim_delete_and_reopen

    proc code1 {tcl} { uplevel #0 $tcl }
  
    # Open connections [db2] and [db3]. Depending on which iteration this
    # is, the connections may be created in this interpreter, or in 
    # interpreters running in other OS processes. As such, the [db2] and [db3]







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# This file contains code used by several different test scripts. The
# code in this file allows testfixture to control another process (or
# processes) to test locking.
#

proc do_multiclient_test {varname script} {

  foreach {tn code} [list 1 {
    if {[info exists ::G(valgrind)]} { db close ; continue }
    set ::code2_chan [launch_testfixture]
    set ::code3_chan [launch_testfixture]
    proc code2 {tcl} { testfixture $::code2_chan $tcl }
    proc code3 {tcl} { testfixture $::code3_chan $tcl }

  } 2 {
    proc code2 {tcl} { uplevel #0 $tcl }
    proc code3 {tcl} { uplevel #0 $tcl }

  }] {
    # Do not run multi-process tests with the unix-excl VFS.
    #
    if {$tn==1 && [permutation]=="unix-excl"} continue

    faultsim_delete_and_reopen

    proc code1 {tcl} { uplevel #0 $tcl }
  
    # Open connections [db2] and [db3]. Depending on which iteration this
    # is, the connections may be created in this interpreter, or in 
    # interpreters running in other OS processes. As such, the [db2] and [db3]

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  Run some tests using the "test_onefile.c" demo
} -initialize {
  set ::G(perm:sqlite3_args) [list -vfs fs]
} -files {
  conflict.test  insert.test   insert2.test  insert3.test
  rollback.test  select1.test  select2.test  select3.test
}











# Run some tests using UTF-16 databases.
#
test_suite "utf16" -description {
  Run tests using UTF-16 databases
} -presql {
  pragma encoding = 'UTF-16'







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} -initialize {
  set ::G(perm:sqlite3_args) [list -vfs fs]
} -files {
  conflict.test  insert.test   insert2.test  insert3.test
  rollback.test  select1.test  select2.test  select3.test
}

# Run some tests using the "unix-excl" VFS.
#
test_suite "unix-excl" -description {
  Run some tests using the "unix-excl" VFS
} -initialize {
  set ::G(perm:sqlite3_args) [list -vfs unix-excl]
} -files {
  shmlock.test
}

# Run some tests using UTF-16 databases.
#
test_suite "utf16" -description {
  Run tests using UTF-16 databases
} -presql {
  pragma encoding = 'UTF-16'

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# 2018 December 6
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl

set testprefix shmlock

ifcapable !wal {finish_test ; return }

sqlite3 db2 test.db
sqlite3 db3 test.db

do_execsql_test 1.0 {
  PRAGMA journal_mode = wal;
  CREATE TABLE t1(a, b);
  INSERT INTO t1 VALUES(1, 2);
} {wal}
do_test 1.1 { execsql { SELECT * FROM t1 } db2 } {1 2}
do_test 1.2 { execsql { SELECT * FROM t1 } db3 } {1 2}

foreach {tn dbhandle cmd res} {
  1    db  {shared    lock   7 1}    OK
  2    db2 {exclusive lock   7 1}    BUSY
  3    db  {shared    unlock 7 1}    OK
  4    db2 {exclusive lock   7 1}    OK
  5    db  {shared    lock   7 1}    BUSY
  6    db  {exclusive lock   7 1}    BUSY
  7    db2 {exclusive unlock 7 1}    OK

  8    db  {exclusive lock   0 8}    OK
  9    db  {exclusive unlock 0 8}    OK
  10   db2 {exclusive lock   0 8}    OK
  11   db2 {exclusive unlock 0 8}    OK

  12   db  {shared    lock   0 1}    OK
  13   db2 {shared    lock   0 1}    OK
  14   db3 {shared    lock   0 1}    OK
  15   db3 {shared    unlock 0 1}    OK
  16   db3 {exclusive lock   0 1}    BUSY
  17   db2 {shared    unlock 0 1}    OK
  18   db3 {exclusive lock   0 1}    BUSY
  19   db  {shared    unlock 0 1}    OK
  20   db3 {exclusive lock   0 1}    OK
  21   db3 {exclusive unlock 0 1}    OK

  22   db  {shared    lock   3 1}    OK
  23   db2 {exclusive lock   2 2}    BUSY
  24   db  {shared    lock   2 1}    OK
  25   db2 {exclusive lock   0 5}    BUSY
  26   db2 {exclusive lock   0 4}    BUSY
  27   db2 {exclusive lock   0 3}    BUSY
  28   db  {shared    unlock 3 1}    OK
  29   db2 {exclusive lock   2 2}    BUSY
  28   db  {shared    unlock 2 1}    OK
  29   db2 {exclusive lock   2 2}    OK
  29   db2 {exclusive unlock 2 2}    OK
} {
  do_test 1.3.$tn [list vfs_shmlock $dbhandle main {*}$cmd] "SQLITE_$res"
}

db  close
db2 close
db3 close

if {[permutation]=="unix-excl"} {
  do_test 2.0 {
    for {set i 0} {$i < 256} {incr i} { 
      sqlite3 db$i test.db 
      execsql { SELECT * FROM t1 } db$i
    }
    for {set i 0} {$i < 255} {incr i} { 
      set rc [vfs_shmlock db$i main shared lock 4 1]
      if {$rc != "SQLITE_OK"} { error $rc }
    }

    vfs_shmlock db255 main shared lock 4 1
  } {SQLITE_BUSY}

  do_test 2.1 { vfs_shmlock db255 main exclusive lock   4 1 } SQLITE_BUSY
  do_test 2.2 { vfs_shmlock db0   main shared    unlock 4 1 } SQLITE_OK
  do_test 2.3 { vfs_shmlock db255 main shared    lock   4 1 } SQLITE_OK
  do_test 2.4 { vfs_shmlock db255 main shared    unlock 4 1 } SQLITE_OK
  do_test 2.5 { vfs_shmlock db255 main exclusive lock   4 1 } SQLITE_BUSY

  do_test 2.6 {
    for {set i 1} {$i < 255} {incr i} { 
      set rc [vfs_shmlock db255 main exclusive lock 4 1]
      if {$rc != "SQLITE_BUSY"} { error $rc }
      set rc [vfs_shmlock db$i main shared unlock 4 1]
      if {$rc != "SQLITE_OK"} { error $rc }
    }

    vfs_shmlock db255 main exclusive lock 4 1
  } {SQLITE_OK}

  vfs_shmlock db255 main exclusive unlock 4 1
}

finish_test


Changes to test/wal.test.

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#
#   3. Using connection 1, checkpoint the database. Make sure all
#      the data is present and the database is not corrupt.
#
# At one point, SQLite was failing to grow the mapping of the wal-index
# file in step 3 and the checkpoint was corrupting the database file.
#

do_test wal-20.1 {
  catch {db close}
  forcedelete test.db test.db-wal test.db-journal
  sqlite3 db test.db
  execsql {
    PRAGMA journal_mode = WAL;
    CREATE TABLE t1(x);
    INSERT INTO t1 VALUES(randomblob(900));
    SELECT count(*) FROM t1;
  }
} {wal 1}
do_test wal-20.2 {
  set ::buddy [launch_testfixture]
  testfixture $::buddy {
    sqlite3 db test.db
    db transaction { db eval {
      PRAGMA wal_autocheckpoint = 0;
      INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 2 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 4 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 8 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 16 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 32 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 64 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 128 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 256 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 512 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 1024 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 2048 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 4096 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 8192 */
      INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 16384 */
    } }
  }
} {0}
do_test wal-20.3 {
  close $::buddy
  execsql { PRAGMA wal_checkpoint }
  execsql { SELECT count(*) FROM t1 }
} {16384}
do_test wal-20.4 {
  db close
  sqlite3 db test.db
  execsql { SELECT count(*) FROM t1 }
} {16384}
integrity_check wal-20.5


catch { db2 close }
catch { db close }

do_test wal-21.1 {
  faultsim_delete_and_reopen
  execsql { 







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#
#   3. Using connection 1, checkpoint the database. Make sure all
#      the data is present and the database is not corrupt.
#
# At one point, SQLite was failing to grow the mapping of the wal-index
# file in step 3 and the checkpoint was corrupting the database file.
#
if {[permutation]!="unix-excl"} {
  do_test wal-20.1 {
    catch {db close}
    forcedelete test.db test.db-wal test.db-journal
    sqlite3 db test.db
    execsql {
      PRAGMA journal_mode = WAL;
      CREATE TABLE t1(x);
      INSERT INTO t1 VALUES(randomblob(900));
      SELECT count(*) FROM t1;
    }
  } {wal 1}
  do_test wal-20.2 {
    set ::buddy [launch_testfixture]
    testfixture $::buddy {
      sqlite3 db test.db
      db transaction { db eval {
        PRAGMA wal_autocheckpoint = 0;
        INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 2 */
        INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 4 */
        INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 8 */
        INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 16 */
        INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 32 */
        INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 64 */
        INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 128 */
        INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 256 */
        INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 512 */
        INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 1024 */
        INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 2048 */
        INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 4096 */
        INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 8192 */
        INSERT INTO t1 SELECT randomblob(900) FROM t1;       /* 16384 */
      } }
    }
  } {0}
  do_test wal-20.3 {
    close $::buddy
    execsql { PRAGMA wal_checkpoint }
    execsql { SELECT count(*) FROM t1 }
  } {16384}
  do_test wal-20.4 {
    db close
    sqlite3 db test.db
    execsql { SELECT count(*) FROM t1 }
  } {16384}
  integrity_check wal-20.5
}

catch { db2 close }
catch { db close }

do_test wal-21.1 {
  faultsim_delete_and_reopen
  execsql {