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Overview
| Comment: | Remove some branches in walTryBeginRead() that were added by check-in [ce5d13c2de] but became unreachable with the addition of logic in check-in [18b26843] that enabled read-only clients to parse the WAL file into a heap-memory WAL-index, thus guaranteeing that the WAL-index header is always available. |
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| Downloads: | Tarball | ZIP archive |
| Timelines: | family | ancestors | descendants | both | readonly-wal-recovery |
| Files: | files | file ages | folders |
| SHA3-256: |
9c6b38b9a96c11bdf9db4ea025720a4f |
| User & Date: | drh 2017-11-13 05:51:37.627 |
Context
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2017-11-14
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| 03:42 | Improvement to a comment. No changes to code. (Closed-Leaf check-in: 486949fc03 user: drh tags: readonly-wal-recovery) | |
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2017-11-13
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| 05:51 | Remove some branches in walTryBeginRead() that were added by check-in [ce5d13c2de] but became unreachable with the addition of logic in check-in [18b26843] that enabled read-only clients to parse the WAL file into a heap-memory WAL-index, thus guaranteeing that the WAL-index header is always available. (check-in: 9c6b38b9a9 user: drh tags: readonly-wal-recovery) | |
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2017-11-11
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| 20:11 | In wal.c: improved comments, new assert() and testcase() macros, and replace some magic numbers with appropriate symbolic constants. (check-in: 13ec8a77a4 user: drh tags: readonly-wal-recovery) | |
Changes
Changes to src/wal.c.
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2414 2415 2416 2417 2418 2419 2420 2421 2422 2423 2424 2425 2426 2427 | int mxI; /* Index of largest aReadMark[] value */ int i; /* Loop counter */ int rc = SQLITE_OK; /* Return code */ u32 mxFrame; /* Wal frame to lock to */ assert( pWal->readLock<0 ); /* Not currently locked */ /* Take steps to avoid spinning forever if there is a protocol error. ** ** Circumstances that cause a RETRY should only last for the briefest ** instances of time. No I/O or other system calls are done while the ** locks are held, so the locks should not be held for very long. But ** if we are unlucky, another process that is holding a lock might get ** paged out or take a page-fault that is time-consuming to resolve, | > > > | 2414 2415 2416 2417 2418 2419 2420 2421 2422 2423 2424 2425 2426 2427 2428 2429 2430 | int mxI; /* Index of largest aReadMark[] value */ int i; /* Loop counter */ int rc = SQLITE_OK; /* Return code */ u32 mxFrame; /* Wal frame to lock to */ assert( pWal->readLock<0 ); /* Not currently locked */ /* useWal may only be set for read/write connections */ assert( (pWal->readOnly & WAL_SHM_RDONLY)==0 || useWal==0 ); /* Take steps to avoid spinning forever if there is a protocol error. ** ** Circumstances that cause a RETRY should only last for the briefest ** instances of time. No I/O or other system calls are done while the ** locks are held, so the locks should not be held for very long. But ** if we are unlucky, another process that is holding a lock might get ** paged out or take a page-fault that is time-consuming to resolve, |
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2480 2481 2482 2483 2484 2485 2486 |
}
else if( pWal->bShmUnreliable ){
return walBeginShmUnreliable(pWal, pChanged);
}
}
assert( pWal->nWiData>0 );
| | | | < | < | 2483 2484 2485 2486 2487 2488 2489 2490 2491 2492 2493 2494 2495 2496 2497 2498 2499 2500 2501 2502 2503 2504 2505 2506 2507 2508 2509 2510 2511 |
}
else if( pWal->bShmUnreliable ){
return walBeginShmUnreliable(pWal, pChanged);
}
}
assert( pWal->nWiData>0 );
assert( pWal->apWiData[0]!=0 );
pInfo = walCkptInfo(pWal);
if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame
#ifdef SQLITE_ENABLE_SNAPSHOT
&& (pWal->pSnapshot==0 || pWal->hdr.mxFrame==0
|| 0==memcmp(&pWal->hdr, pWal->pSnapshot, sizeof(WalIndexHdr)))
#endif
){
/* The WAL has been completely backfilled (or it is empty).
** and can be safely ignored.
*/
rc = walLockShared(pWal, WAL_READ_LOCK(0));
walShmBarrier(pWal);
if( rc==SQLITE_OK ){
if( memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) ){
/* It is not safe to allow the reader to continue here if frames
** may have been appended to the log before READ_LOCK(0) was obtained.
** When holding READ_LOCK(0), the reader ignores the entire log file,
** which implies that the database file contains a trustworthy
** snapshot. Since holding READ_LOCK(0) prevents a checkpoint from
** happening, this is usually correct.
**
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