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Overview
Comment: | Further comment improvements in wal.c. No code changes. |
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Downloads: | Tarball | ZIP archive |
Timelines: | family | ancestors | descendants | both | readonly-wal-recovery |
Files: | files | file ages | folders |
SHA3-256: |
346388007de585083dc67ad865b91db7 |
User & Date: | drh 2017-11-11 13:30:44.595 |
Context
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) | |
13:30 | Further comment improvements in wal.c. No code changes. (check-in: 346388007d user: drh tags: readonly-wal-recovery) | |
2017-11-10
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20:00 | Improved comments and variable names in the read-only WAL logic. (check-in: d3c25740ee user: drh tags: readonly-wal-recovery) | |
Changes
Changes to src/wal.c.
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2226 2227 2228 2229 2230 2231 2232 | pWal->readLock = 0; /* Check to see if a separate writer has attached to the shared-memory area, ** thus making the shared-memory "reliable" again. Do this by invoking ** the xShmMap() routine of the VFS and looking to see if the return ** is SQLITE_READONLY instead of SQLITE_READONLY_CANTINIT. ** | < < < < < < > > > > > > > > > > > > > | | | < < | < < < | 2226 2227 2228 2229 2230 2231 2232 2233 2234 2235 2236 2237 2238 2239 2240 2241 2242 2243 2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254 2255 2256 2257 2258 2259 2260 2261 2262 2263 2264 2265 2266 2267 2268 2269 2270 2271 | pWal->readLock = 0; /* Check to see if a separate writer has attached to the shared-memory area, ** thus making the shared-memory "reliable" again. Do this by invoking ** the xShmMap() routine of the VFS and looking to see if the return ** is SQLITE_READONLY instead of SQLITE_READONLY_CANTINIT. ** ** If the shared-memory is now "reliable" return WAL_RETRY, which will ** cause the heap-memory WAL-index to be discarded and the actual ** shared memory to be used in its place. ** ** This step is important because, even though this connection is holding ** the WAL_READ_LOCK(0) which prevents a checkpoint, a writer might ** have already checkpointed the WAL file and, while the current ** is active, wrap the WAL and start overwriting frames that this ** process wants to use. ** ** Once sqlite3OsShmMap() has been called for an sqlite3_file and has ** returned any SQLITE_READONLY value, it must return only SQLITE_READONLY ** or SQLITE_READONLY_CANTINIT or some error for all subsequent invocations, ** even if some external agent does a "chmod" to make the shared-memory ** writable by us, until sqlite3OsShmUnmap() has been called. ** This is a requirement on the VFS implementation. */ rc = sqlite3OsShmMap(pWal->pDbFd, 0, WALINDEX_PGSZ, 0, &pDummy); assert( rc!=SQLITE_OK ); /* SQLITE_OK not possible for read-only connection */ if( rc!=SQLITE_READONLY_CANTINIT ){ rc = (rc==SQLITE_READONLY ? WAL_RETRY : rc); goto begin_unreliable_shm_out; } /* We reach this point only if the real shared-memory is still unreliable. ** Assume the in-memory WAL-index substitute is correct and load it ** into pWal->hdr. */ memcpy(&pWal->hdr, (void*)walIndexHdr(pWal), sizeof(WalIndexHdr)); /* Make sure some writer hasn't come in and changed the WAL file out ** from under us, then disconnected, while we were not looking. */ rc = sqlite3OsFileSize(pWal->pWalFd, &szWal); if( rc!=SQLITE_OK ){ goto begin_unreliable_shm_out; } if( szWal<WAL_HDRSIZE ){ /* If the wal file is too small to contain a wal-header and the |
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2279 2280 2281 2282 2283 2284 2285 2286 2287 2288 2289 2290 2291 2292 | /* Check the salt keys at the start of the wal file still match. */ rc = sqlite3OsRead(pWal->pWalFd, aBuf, WAL_HDRSIZE, 0); if( rc!=SQLITE_OK ){ goto begin_unreliable_shm_out; } if( memcmp(&pWal->hdr.aSalt, &aBuf[16], 8) ){ rc = WAL_RETRY; goto begin_unreliable_shm_out; } /* Allocate a buffer to read frames into */ szFrame = pWal->hdr.szPage + WAL_FRAME_HDRSIZE; aFrame = (u8 *)sqlite3_malloc64(szFrame); | > > > | 2281 2282 2283 2284 2285 2286 2287 2288 2289 2290 2291 2292 2293 2294 2295 2296 2297 | /* Check the salt keys at the start of the wal file still match. */ rc = sqlite3OsRead(pWal->pWalFd, aBuf, WAL_HDRSIZE, 0); if( rc!=SQLITE_OK ){ goto begin_unreliable_shm_out; } if( memcmp(&pWal->hdr.aSalt, &aBuf[16], 8) ){ /* Some writer has wrapped the WAL file while we were not looking. ** Return WAL_RETRY which will cause the in-memory WAL-index to be ** rebuilt. */ rc = WAL_RETRY; goto begin_unreliable_shm_out; } /* Allocate a buffer to read frames into */ szFrame = pWal->hdr.szPage + WAL_FRAME_HDRSIZE; aFrame = (u8 *)sqlite3_malloc64(szFrame); |
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