答复: [GENERAL] how to calculate or know seq_scan scan how many blocks every time

Hello Craig:
I want to know a sequential scan( full scan table) it can read how many
blocks every io?
I know scan index read is one block every io.

Oracle parameter db_file_multiblock_read_count it can control scattered
read (full scan table),
assume db_file_multiblock_read_count =10,when scan full table,every io
request blocks is 10 blocks.
I know scan index read is one block every io.

So I want to when happen scan full table,postgresql scan full table scan
how many blocks every io?

Thank you!
-----邮件原件-----
发件人: Craig Ringer [mailto:ringerc(at)ringerc(dot)id(dot)au]
发送时间: 2012年7月27日 8:41
收件人: leo xu
抄送: pgsql-general(at)postgresql(dot)org
主题: Re: [GENERAL] how to calculate or know seq_scan scan how many blocks
every time

On 07/25/2012 07:38 PM, leo xu wrote:
> hello:
> i know oracle scatter read blocks,can set
> db_file_multiblock_read_count every time,
> i see postgres,it exists scatter read blocks,it is seq_scan,how to
> know scan many bloks every time?
>

If I understand correctly, you want to have a sequential scan read from more
than one place at once.

This is not currently supported.

The effective_io_concurrency setting would be where you would set it, but it
does not affect sequential scans at the moment.

--
Craig Ringer