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Overview
| Comment: | Enhance the wal2 header comment in wal.c to explain how the wal-hook is invoked in wal2 mode. |
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| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | wal2 |
| Files: | files | file ages | folders |
| SHA3-256: | 118aa7e32a94ad971a955ab60db5bfc5 |
| User & Date: | dan 2018-12-22 15:50:00 |
| Wiki: | wal2 |
Context
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2018-12-26
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| 19:10 | Merge latest trunk changes with this branch. check-in: 404f9d99 user: dan tags: wal2 | |
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2018-12-22
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| 15:50 | Enhance the wal2 header comment in wal.c to explain how the wal-hook is invoked in wal2 mode. check-in: 118aa7e3 user: dan tags: wal2 | |
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2018-12-17
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| 15:22 | Add extra test case to wal2recover.test. check-in: 1a5aa734 user: dan tags: wal2 | |
Changes
Changes to src/wal.c.
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** ** The wal file that writers are currently appending to (the one they ** don't have to check the above two criteria before writing to) is called ** the "current" wal file. ** ** The first wal file takes the same name as the wal file in legacy wal ** mode systems - "<db>-wal". The second is named "<db>-wal2". ** ** WAL FILE FORMAT ** ** The file format used for each wal file in wal2 mode is the same as for ** legacy wal mode. Except, the file format field is set to 3021000 ** instead of 3007000. ** |
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** ** The wal file that writers are currently appending to (the one they ** don't have to check the above two criteria before writing to) is called ** the "current" wal file. ** ** The first wal file takes the same name as the wal file in legacy wal ** mode systems - "<db>-wal". The second is named "<db>-wal2". ** ** CHECKPOINTS ** ** The "pre-configured size" mentioned above is the value set by ** "PRAGMA journal_size_limit". Or, if journal_size_limit is not set, ** 1000 pages. ** ** There is only a single type of checkpoint in wal2 mode (no "truncate", ** "restart" etc.), and it always checkpoints the entire contents of a single ** wal file. A wal file cannot be checkpointed until after a writer has written ** the first transaction into the other wal file and all readers are reading a ** snapshot that includes at least one transaction from the other wal file. ** ** The wal-hook, if one is registered, is invoked after a write-transaction ** is committed, just as it is in legacy wal mode. The integer parameter ** passed to the wal-hook is the total number of uncheckpointed frames in both ** wal files. Except, the parameter is set to zero if there is no frames ** that may be checkpointed. This happens in two scenarios: ** ** 1. The "other" wal file (the one that the writer did not just append to) ** is completely empty, or ** ** 2. The "other" wal file (the one that the writer did not just append to) ** has already been checkpointed. ** ** ** WAL FILE FORMAT ** ** The file format used for each wal file in wal2 mode is the same as for ** legacy wal mode. Except, the file format field is set to 3021000 ** instead of 3007000. ** |