Jeff Davis <pg...@j-davis.com> wrote: > And, if we had a bulk loading path, we could probably get away > with writing the data only twice (today, we write it 3 times > including the hint bits) or maybe once if WAL archiving is off. If you're counting WAL writes, you're low. If you don't go out of your way to avoid it, you are likely to write the data to the table once during the bulk load, a second time on first read to set the hint bits, and a third time to freeze data to prevent wrap-around. The initial write may or may not be WAL-logged. The freezing typically is WAL-logged. So, you can easily write the data to disk four or five times. With luck these are spread out uniformly or happen during off-peak periods. Unmanaged, a WAL-logged freeze of bulk-loaded data is somewhat more likely to occur, however, during hours of heavy OLTP load, because transaction numbers are consumed so quickly. Currently, a VACUUM FREEZE after a bulk load collapses at least two of those writes to one. With luck, some pages might still be dirty in cache, and you can save two of the writes. -Kevin
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