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Re: about multiprocessingmassdata

From: Tomas Vondra <tv(at)fuzzy(dot)cz>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: about multiprocessingmassdata
Date: 2012-04-09 23:50:59
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Lists: pgsql-performance
On 10.4.2012 00:37, Merlin Moncure wrote:
> On Thu, Apr 5, 2012 at 9:47 AM, Tomas Vondra <tv(at)fuzzy(dot)cz> wrote:
>> If you have slower drives, the dependency is about linear (half the
>> speed -> twice the time). So either your drives are very slow, or
>> there's something rotten.
>> I still haven's seen iostat / vmstat output ... that'd tell us much more
>> about the causes.
> geometry column can potentially quite wide.  one thing we need to see
> is the table has any indexes -- in particular gist/gin on the
> geometry.

Yeah, but in one of the previous posts the OP posted this:

relname      | relpages  |  reltuples
poi_all_new |  2421133 | 6.53328e+06

which means the table has ~ 19GB for 6.5 million rows, so it's like
2.8GB per 1 million of rows, i.e. ~3kB per row. I've been working with 1
million rows and 1.3GB of data, so it's like 50% of the expected amount.

But this does not explain why the SELECT COUNT(*) takes 364 seconds on
that machine. That'd mean ~8MB/s.

Regarding the indexes, the the OP already posted a description of the
table and apparently there are these indexes:

    "poi_all_new_pk" PRIMARY KEY, btree (ogc_fid)
    "poi_all_new_flname_idx" btree (flname)
    "poi_all_new_geom_idx" btree (wkb_geometry)
    "poi_all_new_ogc_fid_idx" btree (ogc_fid)
    "poi_all_new_pinyin_idx" btree (pinyin)

So none of them is GIN/GIST although some one of them is on the geometry


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Subject: Re: Planner selects slow "Bitmap Heap Scan" when "Index Scan" is faster
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