Update mmap details:
< portability issues. Anonymous mmap is required to prevent I/O < overhead. > portability issues. Anonymous mmap (or mmap to /dev/zero) is required > to prevent I/O overhead. > > * Consider mmap()'ing files into a backend? > > Doing I/O to large tables would consume a lot of address space or > require frequent mapping/unmapping. Extending the file also causes > mapping problems that might require mapping only individual pages, > leading to thousands of mappings. Another problem is that there is no > way to _prevent_ I/O to disk from the dirty shared buffers so changes > could hit disk before WAL is written.
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@ -6,7 +6,7 @@ TODO list for PostgreSQL
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Bracketed items "[]" have more detail.
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Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
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Last updated: Mon Nov 8 15:16:11 EST 2004
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Last updated: Mon Nov 8 22:57:34 EST 2004
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The most recent version of this document can be viewed at the PostgreSQL web
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site, http://www.PostgreSQL.org.
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@ -815,8 +815,17 @@ Miscellaneous
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* Use mmap() rather than SYSV shared memory or to write WAL files (?) [mmap]
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This would remove the requirement for SYSV SHM but would introduce
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portability issues. Anonymous mmap is required to prevent I/O
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overhead.
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portability issues. Anonymous mmap (or mmap to /dev/zero) is required
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to prevent I/O overhead.
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* Consider mmap()'ing files into a backend?
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Doing I/O to large tables would consume a lot of address space or
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require frequent mapping/unmapping. Extending the file also causes
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mapping problems that might require mapping only individual pages,
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leading to thousands of mappings. Another problem is that there is no
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way to _prevent_ I/O to disk from the dirty shared buffers so changes
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could hit disk before WAL is written.
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* Add a script to ask system configuration questions and tune postgresql.conf
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* Use a phantom command counter for nested subtransactions to reduce
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