| From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Greg Stark <gsstark(at)mit(dot)edu>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Question about indexes |
| Date: | 2004-01-30 15:14:22 |
| Message-ID: | 200401301514.i0UFEMl15556@candle.pha.pa.us |
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| Lists: | pgsql-hackers |
Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > Also, what does an in-memory bitmapped index look like?
>
> One idea that might work: a binary search tree in which each node
> represents a single page of the table, and contains a bit array with
> one bit for each possible item number on the page. You could not need
> more than BLCKSZ/(sizeof(HeapTupleHeaderData)+sizeof(ItemIdData)) bits
> in a node, or about 36 bytes at default BLCKSZ --- for most tables you
> could probably prove it would be a great deal less. You only allocate
> nodes for pages that have at least one interesting row.
Actually, I think I made a mistake. I was wondering what on-disk
bitmapped indexes look like.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
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