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Overview
Comment: | Document the SQLITE_QUERY_PLANNER_LIMIT and SQLITE_QUERY_PLANNER_LIMIT_INCR compile-time options. |
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Downloads: | Tarball | ZIP archive |
Timelines: | family | ancestors | descendants | both | trunk |
Files: | files | file ages | folders |
SHA3-256: |
55fce17e3c1bc014657664e941ec8c99 |
User & Date: | drh 2018-09-24 12:40:44.866 |
Context
2018-09-26
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15:19 | Merge changes from the 3.25 branch. (check-in: 2e3a732177 user: drh tags: trunk) | |
2018-09-24
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12:40 | Document the SQLITE_QUERY_PLANNER_LIMIT and SQLITE_QUERY_PLANNER_LIMIT_INCR compile-time options. (check-in: 55fce17e3c user: drh tags: trunk) | |
2018-09-21
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10:16 | Fix a harmless typo in the json documentation. (check-in: 2bdb2d7e21 user: drh tags: trunk) | |
Changes
Changes to pages/compile.in.
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509 510 511 512 513 514 515 516 517 518 519 520 521 522 | Setting SQLITE_POWERSAFE_OVERWRITE to 1 causes SQLite to assume that application-level writes cannot changes bytes outside the range of bytes written even if the write occurs just before a power loss. With SQLITE_POWERSAFE_OVERWRITE set to 0, SQLite assumes that other bytes in the same sector with a written byte might be changed or damaged by a power loss. } COMPILE_OPTION {SQLITE_REVERSE_UNORDERED_SELECTS} { This option causes the [PRAGMA reverse_unordered_selects] setting to be enabled by default. When enabled, [SELECT] statements that lack an ORDER BY clause will run in reverse order.<p> This option is useful for detecting when applications (incorrectly) assume that the order of rows in a SELECT without an ORDER BY clause | > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 | Setting SQLITE_POWERSAFE_OVERWRITE to 1 causes SQLite to assume that application-level writes cannot changes bytes outside the range of bytes written even if the write occurs just before a power loss. With SQLITE_POWERSAFE_OVERWRITE set to 0, SQLite assumes that other bytes in the same sector with a written byte might be changed or damaged by a power loss. } COMPILE_OPTION {SQLITE_QUERY_PLANNER_LIMIT=<i>N</i>} { As part of the query planning process, SQLite enumerates all usable combinations of indexes and WHERE-clause constraints. For certain pathological queries, the number of these index-and-constraint combinations can be very large, resulting in slow performance by the query planner. The SQLITE_QUERY_PLANNER_LIMIT value (in conjunction with the related [SQLITE_QUERY_PLANNER_LIMIT_INCR] setting) limits the number of index-and-constraint combinations that the query planner will consider, in order to prevent the query planner from using excess CPU time. The default value for SQLITE_QUERY_PLANNER_LIMIT is set high enough so that is never reached for real-world queries. The query planner search limit only applies to queries that are deliberately crafted to use excess planning time. } COMPILE_OPTION {SQLITE_QUERY_PLANNER_LIMIT_INCR=<i>N</i>} { The [SQLITE_QUERY_PLANNER_LIMIT] option sets an initial baseline value for the maximum number of index-and-constraint combinations that the query planner consider. The baseline query planner limit is increased by SQLITE_QUERY_PLANNER_LIMIT_INCR prior to processing each table of a join so that each table is guaranteed to be able to propose at least some index-and-constraint combinations to the optimizer even if prior tables of the join have exhausted the baseline limit. The default value for both this compile-time option and the [SQLITE_QUERY_PLANNER_LIMIT] option are set high enough so that they should never be reached for real-world queries. } COMPILE_OPTION {SQLITE_REVERSE_UNORDERED_SELECTS} { This option causes the [PRAGMA reverse_unordered_selects] setting to be enabled by default. When enabled, [SELECT] statements that lack an ORDER BY clause will run in reverse order.<p> This option is useful for detecting when applications (incorrectly) assume that the order of rows in a SELECT without an ORDER BY clause |
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