Re: Question regarding the database page layout.
От | Ryan Bradetich |
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Тема | Re: Question regarding the database page layout. |
Дата | |
Msg-id | e739902b0809021452t7cebd016n5b5d22049551e129@mail.gmail.com обсуждение исходный текст |
Ответ на | Re: Question regarding the database page layout. (Tom Lane <tgl@sss.pgh.pa.us>) |
Список | pgsql-hackers |
Hello Tom, > Well, as Greg pointed out, setting t_hoff correctly should be sufficient > for squeezing out useless padding between the tuple header and the tuple > data. The real objection here is that that's leaving most of the > possible gain still on the table. The tuple *as a whole* (header and > data both) is still going to get maxaligned when it's plopped onto a > disk page. I think that in real-world cases that's often where the > main padding cost comes in: with 23-byte tuple headers and no OIDs, > you aren't saving a thing by int-aligning t_hoff unless you have a nulls > bitmap and it's the wrong number of bytes long. > > So IMHO the real problem is over near PageAddItem. Thanks for your feed back as well. Between you and Greg I think I finally understand the error in my thinking. I will investigate the PageAddItem() later tonight. - Ryan
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