| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Grzegorz Jaskiewicz <gj(at)pointblue(dot)com(dot)pl> |
| Cc: | "Luke Lonergan" <llonergan(at)greenplum(dot)com>, "PGSQL Hackers" <pgsql-hackers(at)postgresql(dot)org>, "Doug Rady" <drady(at)greenplum(dot)com>, "Sherry Moore" <sherry(dot)moore(at)sun(dot)com> |
| Subject: | Re: Bug: Buffer cache is not scan resistant |
| Date: | 2007-03-05 08:24:11 |
| Message-ID: | 8324.1173083051@sss.pgh.pa.us |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
Grzegorz Jaskiewicz <gj(at)pointblue(dot)com(dot)pl> writes:
> On Mar 5, 2007, at 2:36 AM, Tom Lane wrote:
>> I'm also less than convinced that it'd be helpful for a big seqscan:
>> won't reading a new disk page into memory via DMA cause that memory to
>> get flushed from the processor cache anyway?
> Nope. DMA is writing directly into main memory. If the area was in
> the L2/L1 cache, it will get invalidated. But if it isn't there, it
> is okay.
So either way, it isn't in processor cache after the read. So how can
there be any performance benefit?
regards, tom lane
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Luke Lonergan | 2007-03-05 08:28:49 | Re: Bug: Buffer cache is not scan resistant |
| Previous Message | ITAGAKI Takahiro | 2007-03-05 08:22:16 | Re: Automatic adjustment of bgwriter_lru_maxpages |