| From: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> |
|---|---|
| To: | Slava Moudry <smoudry(at)4info(dot)net> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: number of rows estimation for bit-AND operation |
| Date: | 2009-08-21 01:32:02 |
| Message-ID: | dcc563d10908201832u85305ebg93d014e355a34f@mail.gmail.com |
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| Lists: | pgsql-performance |
2009/8/20 Slava Moudry <smoudry(at)4info(dot)net>:
> Hi,
> Yes, I thought about putting the bit-flags in separate fields.
> Unfortunately - I expect to have quite a lot of these and space is an issue when you are dealing with billions of records in fact table, so I prefer to pack them into one int8.
For giggles I created two test tables, one with a single int, one with
8 bools, and put 100M entries in each. The table with 8 bools took up
aprrox. 3560616 bytes, while the one with a single int took up approx.
3544212
I.e they're about the same. You should really test to see if having a
lot of bools costs more than mangling ints around. I'm guessing I
could fit a lot more bools in the test table due to alignment issues
than just 8.
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