Re: how to reach D5 in tuplesort.c 's polyphase merge algorithm? - Mailing list pgsql-hackers

From 土卜皿
Subject Re: how to reach D5 in tuplesort.c 's polyphase merge algorithm?
Date
Msg-id CADT5_18YOODbi71=8W8wQW_0MBjkpTz5hfVKf32+TByYTx1cWA@mail.gmail.com
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In response to Re: how to reach D5 in tuplesort.c 's polyphase merge algorithm?  (土卜皿 <pengcz.nwpu@gmail.com>)
List pgsql-hackers
hi,
   I got the same result after work_mem = 64,
but I can get to D5 and D6 after using bigger data sample (at least 100000 records) as Tom said!




2014-07-19 6:35 GMT+08:00 土卜皿 <pengcz.nwpu@gmail.com>:

2014-07-19 6:26 GMT+08:00 Tom Lane <tgl@sss.pgh.pa.us>:

土卜皿 <pengcz.nwpu@gmail.com> writes:
>   for studying polyphase merge algorithm of tuplesort.c, I use ddd and
> apend a table, which has a schema as follows:
> ...
> and has 36684 records, and every record is like:
> id          code  article  name      department
> 31800    266    \N    Machault    77

> and for getting into external sort, I type the following command:

> select * from towns order by name desc;

> but I found it need not reach D5 and D6 during sorting,

That doesn't sound like enough data to force it to spill to disk at all;
at least not unless you turn down work_mem to some very small value.

 
hi, Tom
  thanks a lot!

                 
work_mem you said remind me one more thing I did, I tried to change BLCKSZ = 8192/2, and successfully compiled, but I got a error when executing initdb

Dillon

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