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Overview
Comment: | Add comments to better explain the two-pass memory allocation approach for prepared statements. |
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Downloads: | Tarball | ZIP archive |
Timelines: | family | ancestors | descendants | both | trunk |
Files: | files | file ages | folders |
SHA1: |
0e5e18ea12c70559d4c63981c0bb5f94 |
User & Date: | drh 2009-12-08 19:58:20.000 |
Context
2009-12-08
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22:16 | Change to order of two branches in vtab.c in order to a restore 100% test coverage. (check-in: fdfdc777c5 user: drh tags: trunk) | |
19:58 | Add comments to better explain the two-pass memory allocation approach for prepared statements. (check-in: 0e5e18ea12 user: drh tags: trunk) | |
19:05 | Add tests to improve coverage of fts3. Associated bugfixes. (check-in: f0eac4175a user: dan tags: trunk) | |
Changes
Changes to src/vdbeaux.c.
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1262 1263 1264 1265 1266 1267 1268 | ** NULL, it means that memory space has already been allocated and that ** this routine should not allocate any new memory. When pBuf is not ** NULL simply return pBuf. Only allocate new memory space when pBuf ** is NULL. ** ** nByte is the number of bytes of space needed. ** | | | > | 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 | ** NULL, it means that memory space has already been allocated and that ** this routine should not allocate any new memory. When pBuf is not ** NULL simply return pBuf. Only allocate new memory space when pBuf ** is NULL. ** ** nByte is the number of bytes of space needed. ** ** *ppFrom points to available space and pEnd points to the end of the ** available space. When space is allocated, *ppFrom is advanced past ** the end of the allocated space. ** ** *pnByte is a counter of the number of bytes of space that have failed ** to allocate. If there is insufficient space in *ppFrom to satisfy the ** request, then increment *pnByte by the amount of the request. */ static void *allocSpace( void *pBuf, /* Where return pointer will be stored */ |
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1344 1345 1346 1347 1348 1349 1350 | /* Allocate space for memory registers, SQL variables, VDBE cursors and ** an array to marshal SQL function arguments in. This is only done the ** first time this function is called for a given VDBE, not when it is ** being called from sqlite3_reset() to reset the virtual machine. */ if( nVar>=0 && ALWAYS(db->mallocFailed==0) ){ | | | | > > > > > > > > > > > | 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 | /* Allocate space for memory registers, SQL variables, VDBE cursors and ** an array to marshal SQL function arguments in. This is only done the ** first time this function is called for a given VDBE, not when it is ** being called from sqlite3_reset() to reset the virtual machine. */ if( nVar>=0 && ALWAYS(db->mallocFailed==0) ){ u8 *zCsr = (u8 *)&p->aOp[p->nOp]; /* Memory avaliable for alloation */ u8 *zEnd = (u8 *)&p->aOp[p->nOpAlloc]; /* First byte past available mem */ int nByte; /* How much extra memory needed */ resolveP2Values(p, &nArg); p->usesStmtJournal = (u8)usesStmtJournal; if( isExplain && nMem<10 ){ nMem = 10; } memset(zCsr, 0, zEnd-zCsr); zCsr += (zCsr - (u8*)0)&7; assert( EIGHT_BYTE_ALIGNMENT(zCsr) ); /* Memory for registers, parameters, cursor, etc, is allocated in two ** passes. On the first pass, we try to reuse unused space at the ** end of the opcode array. If we are unable to satisfy all memory ** requirements by reusing the opcode array tail, then the second ** pass will fill in the rest using a fresh allocation. ** ** This two-pass approach that reuses as much memory as possible from ** the leftover space at the end of the opcode array can significantly ** reduce the amount of memory held by a prepared statement. */ do { nByte = 0; p->aMem = allocSpace(p->aMem, nMem*sizeof(Mem), &zCsr, zEnd, &nByte); p->aVar = allocSpace(p->aVar, nVar*sizeof(Mem), &zCsr, zEnd, &nByte); p->apArg = allocSpace(p->apArg, nArg*sizeof(Mem*), &zCsr, zEnd, &nByte); p->azVar = allocSpace(p->azVar, nVar*sizeof(char*), &zCsr, zEnd, &nByte); p->apCsr = allocSpace(p->apCsr, nCursor*sizeof(VdbeCursor*), |
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