| From: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
|---|---|
| To: | ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp> |
| Cc: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, Martijn van Oosterhout <kleptog(at)svana(dot)org>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Free space management within heap page |
| Date: | 2007-01-23 13:18:55 |
| Message-ID: | 45B60B3F.2030707@enterprisedb.com |
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| Lists: | pgsql-hackers |
ITAGAKI Takahiro wrote:
> BLCKSZ is typically 8192 bytes and sizeof(ItemPointerData) is 4 bytes.
> 1/4 comes from 8192 / 4 = 2048. If we allow zero-size tuples, the line
> pointers area can bloat up to the ratio. We have tuples no less than
> 32 bytes-size, so the area is restricted 256 bytes now.
sizeof(ItemPointerData) == 6 bytes
> We can recycle unused line pointers, but we cannot shrink the area unless
> the tail end of line pointers are removed. i.e, unusable free space will
> remains at the middle of LP area.
Yeah, agreed. It'd still be a good idea to do it when possible.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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