Jignesh Shah <jks...@gmail.com> wrote: > When we use Doublewrite with checksums, we can safely disable > full_page_write causing a HUGE reduction to the WAL traffic > without loss of reliatbility due to a write fault since there are > two writes always. (Implementation detail discussable). The "always" there surprised me. It seemed to me that we only need to do the double-write where we currently do full page writes or unlogged writes. In thinking about your message, it finally struck me that this might require a WAL record to be written with the checksum (or CRC; whatever we use). Still, writing a WAL record with a CRC prior to the page write would be less data than the full page. Doing double-writes instead for situations without the torn page risk seems likely to be a net performance loss, although I have no benchmarks to back that up (not having a double-write implementation to test). And if we can get correct behavior without doing either (the checksum WAL record or the double-write), that's got to be a clear win. -Kevin
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