# Writers do not block checkpoints any more either.
  #
  do_test wal-10.$tn.14 {
    catchsql { PRAGMA wal_checkpoint } 
  } {0 {}}

  # Similar to the test above. Except this time, a new read transaction is
  # started (db3) while the checkpointer is waiting for an old one (db2) to 
  # finish. The checkpointer can finish, but any subsequent write operations 
  # must wait until after db3 has closed the read transaction, as db3 is a
  # "region D" writer.
  #
  do_test wal-10.$tn.15 {
    sql2 { COMMIT; BEGIN; SELECT * FROM t1; }
  } {1 2 3 4 5 6 7 8 9 10 11 12}
  do_test wal-10.$tn.16 {
    catchsql { PRAGMA wal_checkpoint } 
  } {1 {database is locked}}
  proc busyhandler x {
    if {$x==3} { sql3 { BEGIN; SELECT * FROM t1 } }
    if {$x==4} { sql2 COMMIT }
    if {$x<5}  { return 0 }
    return 1
  }
  db busy busyhandler
  do_test wal-10.$tn.17 {
    execsql { PRAGMA wal_checkpoint } 
  } {}
  do_test wal-10.$tn.18 {
    sql3 { SELECT * FROM t1 }
  } {1 2 3 4 5 6 7 8 9 10 11 12}
  do_test wal-10.$tn.19 {
    catchsql { INSERT INTO t1 VALUES(13, 14) }
  } {1 {database is locked}}
  do_test wal-10.$tn.20 {
    execsql { SELECT * FROM t1 }
  } {1 2 3 4 5 6 7 8 9 10 11 12}
  do_test wal-10.$tn.21 {
    sql3 COMMIT

  } {}
  do_test wal-10.$tn.22 {
    execsql { INSERT INTO t1 VALUES(13, 14) }
    execsql { SELECT * FROM t1 }
  } {1 2 3 4 5 6 7 8 9 10 11 12 13 14}

  # Set [db3] up as a "region D" reader again. Then upgrade it to a writer
  # and back down to a reader. Then, check that a checkpoint is not possible
  # (as [db3] still has a snapshot locked).
  #
  do_test wal-10.$tn.23 {
    execsql { PRAGMA wal_checkpoint }
  } {}
  do_test wal-10.$tn.24 {
    sql2 { BEGIN; SELECT * FROM t1; }
  } {1 2 3 4 5 6 7 8 9 10 11 12 13 14}
  do_test wal-10.$tn.25 {
    execsql { PRAGMA wal_checkpoint }
  } {}
  do_test wal-10.$tn.26 {
    catchsql { INSERT INTO t1 VALUES(15, 16) }
  } {1 {database is locked}}
  do_test wal-10.$tn.27 {
    sql3 { INSERT INTO t1 VALUES(15, 16) }
  } {}
  do_test wal-10.$tn.28 {
    code3 {
      set ::STMT [sqlite3_prepare db3 "SELECT * FROM t1" -1 TAIL]
      sqlite3_step $::STMT
    }
    sql3 COMMIT
    execsql { SELECT * FROM t1 }
  } {1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16}
  db busy {}
  do_test wal-10.$tn.29 {
    execsql { INSERT INTO t1 VALUES(17, 18) }
    catchsql { PRAGMA wal_checkpoint }
  } {1 {database is locked}}

  do_test wal-10.$tn.30 {
    code3 { sqlite3_finalize $::STMT }
    execsql { PRAGMA wal_checkpoint }
  } {}

  # At one point, if a reader failed to upgrade to a writer because it
  # was reading an old snapshot, the write-locks were not being released.
  # Test that this bug has been fixed.
  #
  do_test wal-10.$tn.31 {

    execsql { BEGIN ; SELECT * FROM t1 }
    sql2 { INSERT INTO t1 VALUES(19, 20) }
    catchsql { INSERT INTO t1 VALUES(21, 22) }
  } {1 {database is locked}}
  do_test wal-10.$tn.32 {
    # This statement would fail when the bug was present.
    sql2 { INSERT INTO t1 VALUES(21, 22) }
  } {}
  do_test wal-10.$tn.33 {
    execsql { SELECT * FROM t1 ; COMMIT }
  } {1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18}
  do_test wal-10.$tn.34 {
    execsql { SELECT * FROM t1 }
  } {1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22}

  # Test that if a checkpointer cannot obtain the required locks, it
  # releases all locks before returning a busy error.
  #
  do_test wal-10.$tn.35 {
    execsql { 
      DELETE FROM t1;
................................................................................
      INSERT INTO t1 VALUES('c', 'd');
    }
    sql2 {
      BEGIN;
        SELECT * FROM t1;
    }
  } {a b c d}
  proc busyhandler x { return 1 }
  db busy busyhandler
  do_test wal-10.$tn.36 {
    catchsql { PRAGMA wal_checkpoint }
  } {1 {database is locked}}

  do_test wal-10.$tn.36 {
    sql3 { INSERT INTO t1 VALUES('e', 'f') }
    sql2 { SELECT * FROM t1 }
  } {a b c d}
  do_test wal-10.$tn.37 {
    sql2 COMMIT
    execsql { PRAGMA wal_checkpoint }

  # Writers do not block checkpoints any more either.
  #
  do_test wal-10.$tn.14 {
    catchsql { PRAGMA wal_checkpoint } 
  } {0 {}}

  # The following series of test cases used to verify another blocking
  # case in WAL - a case which no longer blocks.



  #
  do_test wal-10.$tn.15 {
    sql2 { COMMIT; BEGIN; SELECT * FROM t1; }
  } {1 2 3 4 5 6 7 8 9 10 11 12}
  do_test wal-10.$tn.16 {
    catchsql { PRAGMA wal_checkpoint } 
  } {0 {}}







  do_test wal-10.$tn.17 {
    execsql { PRAGMA wal_checkpoint } 
  } {}
  do_test wal-10.$tn.18 {
    sql3 { BEGIN; SELECT * FROM t1 }
  } {1 2 3 4 5 6 7 8 9 10 11 12}
  do_test wal-10.$tn.19 {
    catchsql { INSERT INTO t1 VALUES(13, 14) }
  } {0 {}}
  do_test wal-10.$tn.20 {
    execsql { SELECT * FROM t1 }
  } {1 2 3 4 5 6 7 8 9 10 11 12 13 14}
  do_test wal-10.$tn.21 {
    sql3 COMMIT
    sql2 COMMIT
  } {}
  do_test wal-10.$tn.22 {

    execsql { SELECT * FROM t1 }
  } {1 2 3 4 5 6 7 8 9 10 11 12 13 14}

  # Another series of tests that used to demonstrate blocking behavior
  # but which now work.

  #
  do_test wal-10.$tn.23 {
    execsql { PRAGMA wal_checkpoint }
  } {}
  do_test wal-10.$tn.24 {
    sql2 { BEGIN; SELECT * FROM t1; }
  } {1 2 3 4 5 6 7 8 9 10 11 12 13 14}
  do_test wal-10.$tn.25 {
    execsql { PRAGMA wal_checkpoint }
  } {}
  do_test wal-10.$tn.26 {
    catchsql { INSERT INTO t1 VALUES(15, 16) }
  } {0 {}}
  do_test wal-10.$tn.27 {
    sql3 { INSERT INTO t1 VALUES(17, 18) }
  } {}
  do_test wal-10.$tn.28 {
    code3 {
      set ::STMT [sqlite3_prepare db3 "SELECT * FROM t1" -1 TAIL]
      sqlite3_step $::STMT
    }

    execsql { SELECT * FROM t1 }
  } {1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18}

  do_test wal-10.$tn.29 {
    execsql { INSERT INTO t1 VALUES(19, 20) }
    catchsql { PRAGMA wal_checkpoint }

  } {0 {}}
  do_test wal-10.$tn.30 {
    code3 { sqlite3_finalize $::STMT }
    execsql { PRAGMA wal_checkpoint }
  } {}

  # At one point, if a reader failed to upgrade to a writer because it
  # was reading an old snapshot, the write-locks were not being released.
  # Test that this bug has been fixed.
  #
  do_test wal-10.$tn.31 {
    sql2 COMMIT
    execsql { BEGIN ; SELECT * FROM t1 }
    sql2 { INSERT INTO t1 VALUES(21, 22) }
    catchsql { INSERT INTO t1 VALUES(23, 24) }
  } {1 {database is locked}}
  do_test wal-10.$tn.32 {
    # This statement would fail when the bug was present.
    sql2 { INSERT INTO t1 VALUES(23, 24) }
  } {}
  do_test wal-10.$tn.33 {
    execsql { SELECT * FROM t1 ; COMMIT }
  } {1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20}
  do_test wal-10.$tn.34 {
    execsql { SELECT * FROM t1 }
  } {1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24}

  # Test that if a checkpointer cannot obtain the required locks, it
  # releases all locks before returning a busy error.
  #
  do_test wal-10.$tn.35 {
    execsql { 
      DELETE FROM t1;
................................................................................
      INSERT INTO t1 VALUES('c', 'd');
    }
    sql2 {
      BEGIN;
        SELECT * FROM t1;
    }
  } {a b c d}


  do_test wal-10.$tn.36 {
    catchsql { PRAGMA wal_checkpoint }

  } {0 {}}
  do_test wal-10.$tn.36 {
    sql3 { INSERT INTO t1 VALUES('e', 'f') }
    sql2 { SELECT * FROM t1 }
  } {a b c d}
  do_test wal-10.$tn.37 {
    sql2 COMMIT
    execsql { PRAGMA wal_checkpoint }