/ Check-in [5343060b]
Login

Many hyperlinks are disabled.
Use anonymous login to enable hyperlinks.

Overview
Comment:Return SQLITE_BUSY (not SQLITE_BUSY_SNAPSHOT) if sqlite3_snapshot_open() fails to obtain the shared checkpointer lock.
Downloads: Tarball | ZIP archive | SQL archive
Timelines: family | ancestors | descendants | both | snapshot-get
Files: files | file ages | folders
SHA1: 5343060bcc6c99029f731f8020d2cba3f405f207
User & Date: dan 2015-12-10 19:11:34
Context
2015-12-10
19:44
Add tests to snapshot.test. check-in: f3b74362 user: dan tags: snapshot-get
19:11
Return SQLITE_BUSY (not SQLITE_BUSY_SNAPSHOT) if sqlite3_snapshot_open() fails to obtain the shared checkpointer lock. check-in: 5343060b user: dan tags: snapshot-get
18:06
Add tests to ensure that an sqlite3_snapshot_open() client cannot be tricked into reading a corrupt snapshot even if another process fails mid-checkpoint. check-in: b908048b user: dan tags: snapshot-get
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/wal.c.

2428
2429
2430
2431
2432
2433
2434

2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451


2452
2453
2454
2455
2456
2457
2458
      ** snapshot X, where X is later in the wal file than pSnapshot, but 
      ** has not yet set the pInfo->nBackfillAttempted variable to indicate 
      ** its intent. To avoid the race condition this leads to, ensure that
      ** there is no checkpointer process by taking a shared CKPT lock 
      ** before checking pInfo->nBackfillAttempted.  */
      rc = walLockShared(pWal, WAL_CKPT_LOCK);


      /* Check that the wal file has not been wrapped. Assuming that it has
      ** not, also check that no checkpointer has attempted to checkpoint
      ** any frames beyond pSnapshot->mxFrame. If either of these conditions
      ** are true, return SQLTIE_BUSY_SNAPSHOT. Otherwise, overwrite pWal->hdr
      ** with *pSnapshot and set *pChanged as appropriate for opening the
      ** snapshot.  */
      if( memcmp(pSnapshot->aSalt, pWal->hdr.aSalt, sizeof(pWal->hdr.aSalt))==0
       && pSnapshot->mxFrame>=pInfo->nBackfillAttempted
      ){
        memcpy(&pWal->hdr, pSnapshot, sizeof(WalIndexHdr));
        *pChanged = bChanged;
      }else{
        rc = SQLITE_BUSY_SNAPSHOT;
      }

      /* Release the shared CKPT lock obtained above. */
      walUnlockShared(pWal, WAL_CKPT_LOCK);



      if( rc!=SQLITE_OK ){
        sqlite3WalEndReadTransaction(pWal);
      }
    }
  }
#endif







>
|
|
|
|
|
|
|
|
|
|
|
|
|
|

|
|
>
>







2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
      ** snapshot X, where X is later in the wal file than pSnapshot, but 
      ** has not yet set the pInfo->nBackfillAttempted variable to indicate 
      ** its intent. To avoid the race condition this leads to, ensure that
      ** there is no checkpointer process by taking a shared CKPT lock 
      ** before checking pInfo->nBackfillAttempted.  */
      rc = walLockShared(pWal, WAL_CKPT_LOCK);

      if( rc==SQLITE_OK ){
        /* Check that the wal file has not been wrapped. Assuming that it has
        ** not, also check that no checkpointer has attempted to checkpoint any
        ** frames beyond pSnapshot->mxFrame. If either of these conditions are
        ** true, return SQLITE_BUSY_SNAPSHOT. Otherwise, overwrite pWal->hdr
        ** with *pSnapshot and set *pChanged as appropriate for opening the
        ** snapshot.  */
        if( !memcmp(pSnapshot->aSalt, pWal->hdr.aSalt, sizeof(pWal->hdr.aSalt))
         && pSnapshot->mxFrame>=pInfo->nBackfillAttempted
        ){
          memcpy(&pWal->hdr, pSnapshot, sizeof(WalIndexHdr));
          *pChanged = bChanged;
        }else{
          rc = SQLITE_BUSY_SNAPSHOT;
        }

        /* Release the shared CKPT lock obtained above. */
        walUnlockShared(pWal, WAL_CKPT_LOCK);
      }


      if( rc!=SQLITE_OK ){
        sqlite3WalEndReadTransaction(pWal);
      }
    }
  }
#endif

Changes to test/snapshot.test.

241
242
243
244
245
246
247
248












































249
250
    BEGIN;
  }
  list [catch {sqlite3_snapshot_open db main $snapshot} msg] $msg
} {1 SQLITE_BUSY_SNAPSHOT}
do_test 4.2.4 {
  sqlite3_snapshot_free $snapshot
} {}













































finish_test









>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>


241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
    BEGIN;
  }
  list [catch {sqlite3_snapshot_open db main $snapshot} msg] $msg
} {1 SQLITE_BUSY_SNAPSHOT}
do_test 4.2.4 {
  sqlite3_snapshot_free $snapshot
} {}

#-------------------------------------------------------------------------
# Check that SQLITE_BUSY is returned if a checkpoint is running when
# sqlite3_snapshot_open() is called.
#
reset_db
db close
testvfs tvfs
sqlite3 db test.db -vfs tvfs

do_execsql_test 5.1 {
  PRAGMA journal_mode = wal;
  CREATE TABLE x1(x, xx, xxx);
  INSERT INTO x1 VALUES('z', 'zz', 'zzz');
  BEGIN;
    SELECT * FROM x1;
} {wal z zz zzz}

do_test 5.2 {
  set ::snapshot [sqlite3_snapshot_get db main]
  sqlite3 db2 test.db -vfs tvfs
  execsql {
    INSERT INTO x1 VALUES('a', 'aa', 'aaa');
    COMMIT;
  }
} {}

set t53 0
proc write_callback {args} {
breakpoint
  do_test 5.3.[incr ::t53] {
    execsql BEGIN
    list [catch { sqlite3_snapshot_open db main $::snapshot } msg] $msg
  } {1 SQLITE_BUSY}
  catchsql COMMIT
}

tvfs filter xWrite
tvfs script write_callback
db2 eval { PRAGMA wal_checkpoint }
db close
db2 close
tvfs delete
sqlite3_snapshot_free $snapshot

finish_test