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Changes In Branch snapshots-lock-wal Excluding Merge-Ins

This is equivalent to a diff from 2c03d8b8 to d71eeaab

2017-11-28
13:39
Lock the wal file for all snapshot transactions, even if they would not otherwise require this, preventing checkpointers and writers from wrapping the wal file. This means that if one connection has an open snapshot transaction it is guaranteed that a second connection can open a transaction on the same snapshot. (check-in: b81a3149 user: dan tags: trunk)
2017-09-25
09:37
Add an extra snapshot related test case. (check-in: 24a95e14 user: dan tags: trunk)
2017-09-23
07:46
Experimental change so that snapshot transactions always lock the wal file - preventing writers or truncate-checkpointers from wrapping it. (Closed-Leaf check-in: d71eeaab user: dan tags: snapshots-lock-wal)
2017-09-22
20:18
Merge in all the trunk enhancements of the previous 7 months. The LIKE optimization has stopped working when there is an ESCAPE - that problem will be addressed in a subsequent check-in. (Leaf check-in: 8d2a1cca user: drh tags: est_count_pragma)
16:23
Use the updated Win32 VFS semantics for winOpen from check-in [5d03c738e9] for WinRT, et al, as well. (check-in: 2c03d8b8 user: mistachkin tags: trunk)
12:52
Partial backout of check-in [e0af9a904076]. It turns out we do need some extra space at the end of the record blob as an overrun area to use when decoding a maliciously malformed record. (check-in: 403b88a8 user: drh tags: trunk)

Changes to src/wal.c.

  2246   2246         return rc;
  2247   2247       }
  2248   2248     }
  2249   2249   
  2250   2250     pInfo = walCkptInfo(pWal);
  2251   2251     if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame 
  2252   2252   #ifdef SQLITE_ENABLE_SNAPSHOT
  2253         -   && (pWal->pSnapshot==0 || pWal->hdr.mxFrame==0
  2254         -     || 0==memcmp(&pWal->hdr, pWal->pSnapshot, sizeof(WalIndexHdr)))
         2253  +   && (pWal->pSnapshot==0 || pWal->hdr.mxFrame==0)
  2255   2254   #endif
  2256   2255     ){
  2257   2256       /* The WAL has been completely backfilled (or it is empty).
  2258   2257       ** and can be safely ignored.
  2259   2258       */
  2260   2259       rc = walLockShared(pWal, WAL_READ_LOCK(0));
  2261   2260       walShmBarrier(pWal);

Added test/snapshot3.test.

            1  +# 2016 September 23
            2  +#
            3  +# The author disclaims copyright to this source code.  In place of
            4  +# a legal notice, here is a blessing:
            5  +#
            6  +#    May you do good and not evil.
            7  +#    May you find forgiveness for yourself and forgive others.
            8  +#    May you share freely, never taking more than you give.
            9  +#
           10  +#***********************************************************************
           11  +# This file implements regression tests for SQLite library. The focus
           12  +# of this file is the sqlite3_snapshot_xxx() APIs.
           13  +#
           14  +
           15  +set testdir [file dirname $argv0]
           16  +source $testdir/tester.tcl
           17  +ifcapable !snapshot {finish_test; return}
           18  +set testprefix snapshot3
           19  +
           20  +# This test does not work with the inmemory_journal permutation. The reason
           21  +# is that each connection opened as part of this permutation executes
           22  +# "PRAGMA journal_mode=memory", which fails if the database is in wal mode
           23  +# and there are one or more existing connections.
           24  +if {[permutation]=="inmemory_journal"} {
           25  +  finish_test
           26  +  return
           27  +}
           28  +
           29  +#-------------------------------------------------------------------------
           30  +# This block of tests verifies that it is not possible to wrap the wal
           31  +# file - using a writer or a "PRAGMA wal_checkpoint = TRUNCATE" - while
           32  +# there is an open snapshot transaction (transaction opened using
           33  +# sqlite3_snapshot_open()).
           34  +#
           35  +do_execsql_test 1.0 {
           36  +  CREATE TABLE t1(y);
           37  +  PRAGMA journal_mode = wal;
           38  +  INSERT INTO t1 VALUES(1);
           39  +  INSERT INTO t1 VALUES(2);
           40  +  INSERT INTO t1 VALUES(3);
           41  +  INSERT INTO t1 VALUES(4);
           42  +} {wal}
           43  +
           44  +do_test 1.1 {
           45  +  sqlite3 db2 test.db
           46  +  sqlite3 db3 test.db
           47  +
           48  +  execsql {SELECT * FROM sqlite_master} db2
           49  +  execsql {SELECT * FROM sqlite_master} db3
           50  +
           51  +  db2 trans { set snap [sqlite3_snapshot_get_blob db2 main] }
           52  +  db2 eval { SELECT * FROM t1 }
           53  +} {1 2 3 4}
           54  +
           55  +do_test 1.2 {
           56  +  execsql BEGIN db2
           57  +  sqlite3_snapshot_open_blob db2 main $snap
           58  +  db2 eval { SELECT * FROM t1 }
           59  +} {1 2 3 4}
           60  +
           61  +do_test 1.2 {
           62  +  execsql END db2
           63  +  execsql { PRAGMA wal_checkpoint }
           64  +
           65  +  execsql BEGIN db2
           66  +  sqlite3_snapshot_open_blob db2 main $snap
           67  +  db2 eval { SELECT * FROM t1 }
           68  +} {1 2 3 4}
           69  +
           70  +set sz [file size test.db-wal]
           71  +do_test 1.3 {
           72  +  execsql { PRAGMA wal_checkpoint = truncate }
           73  +  file size test.db-wal
           74  +} $sz
           75  +
           76  +do_test 1.4 {
           77  +  execsql BEGIN db3
           78  +  list [catch { sqlite3_snapshot_open_blob db3 main $snap } msg] $msg
           79  +} {0 {}}
           80  +
           81  +do_test 1.5 {
           82  +  db3 eval { SELECT * FROM t1; END }
           83  +} {1 2 3 4}
           84  +
           85  +do_test 1.6 {
           86  +  db2 eval { SELECT * FROM t1; END }
           87  +} {1 2 3 4}
           88  +
           89  +do_test 1.7 {
           90  +  execsql { PRAGMA wal_checkpoint = truncate }
           91  +  file size test.db-wal
           92  +} 0
           93  +
           94  +do_test 1.8 {
           95  +  execsql BEGIN db3
           96  +  list [catch { sqlite3_snapshot_open_blob db3 main $snap } msg] $msg
           97  +} {1 SQLITE_BUSY_SNAPSHOT}
           98  +
           99  +finish_test
          100  +