Date: Fri, 7 Mar 2003 15:03:01 -0200 (GMT+2)
From: Achilleus Mantzios <achill@matrix.gatewaynet.com>
To: Andre Schubert <andre@km3.de>
Cc: pgsql-sql@postgresql.org
Subject: Re: Help on indexing timestamps
In-Reply-To: <20030307134702.135fa254.andre@km3.de>
Message-ID: <Pine.LNX.4.44.0303071458080.22117-100000@matrix.gatewaynet.com>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII

On Fri, 7 Mar 2003, Andre Schubert wrote:

> On Fri, 7 Mar 2003 14:17:36 -0200 (GMT+2)
> Achilleus Mantzios <achill@matrix.gatewaynet.com> wrote:
> 
> > On Fri, 7 Mar 2003, Andre Schubert wrote:
> > 
> > > On Fri, 7 Mar 2003 13:48:04 -0200 (GMT+2)
> > > Achilleus Mantzios <achill@matrix.gatewaynet.com> wrote:
> > > 
> > > > On Fri, 7 Mar 2003, Andre Schubert wrote:
> > > > 
> > > > > On Fri, 7 Mar 2003 13:01:16 -0200 (GMT+2)
> > > > > Achilleus Mantzios <achill@matrix.gatewaynet.com> wrote:
> > > > > 
> > > > > > On Fri, 7 Mar 2003, Andre Schubert wrote:
> > > > > > 
> > > > > > > Hi all,
> > > > > > > 
> > > > > > > i have a little problem on indexing a table which contains
> > > > > > > about 4 millions of traffic-data.
> > > > > > > My problem is, that a want to select all data from
> > > > > > > a specific month from a specific ip and this select should use the index.
> > > > > > > I use the following select:
> > > > > > 
> > > > > > Did you try to use BETWEEN ??
> > > > > > E.g.
> > > > > > ... and time_stamp between '2003-01-01 00:00:00'::timestamp and 
> > > > > > '2003-02-01 00:00:00'::timestamp
> > > > > > 
> > > > > 
> > > > > Yes and it works if i write the dates by hand, every new month.
> > > > > But the query is executed automatically and i dont want
> > > > > to write in the dates before the query is executed. Maybe the
> > > > > the start and enddate should also be alculated with sql,
> > > > > because i want to create a view from this statement and execute it every month.
> > > > > Or did i miss something.
> > > > 
> > > > You could have an index on the 
> > > > whole 
> > > > date_trunc('month',tbl_traffic.time_stamp),ip
> > > > 
> > > > How does it perform?
> > > > 
> > > 
> > > I'am not sure how to create such an index...
> > > 
> > > First: create or replace function trunc_ip(timestamp with time zone) returns timestamptz as 
> > >        'select date_trunc(''month'',$1)' language 'sql' with (iscachable);
> > > Then: create index idx_test on tbl_traffic using btree( trunc(time_stamp) );
> > > 
> > > Result: db_km3aue=# explain analyze select sum(inet_up+inet_down) from tbl_traffic where trunc(tbl_traffic.time_stamp) = trunc('2003-02-01'::timestamptz) and ip = '80.243.40.56';
> > > NOTICE:  QUERY PLAN:
> > > 
> > > Aggregate  (cost=108.78..108.78 rows=1 width=16) (actual time=2278.48..2278.48 rows=1 loops=1)
> > >   ->  Index Scan using idx_test on tbl_traffic  (cost=0.00..108.78 rows=1 width=16) (actual time=0.23..2240.50 rows=5346 loops=1)
> > > Total runtime: 2278.62 msec
> > > 
> > > Maybe the problem is, that the index is created without ip as the second column....
> > 
> > Sorry, it sliped my mind that we cannot have compound indexes on 
> > functions. :(
> > 
> > Anyway.
> > Did the explicit BETWEEN gave you satisfactory performance?
> > 
> 
> Yes if i use BETWEEN and type in the dates by hand the query takes about 200ms with explain analyze.
> I think these is a good performance.
> But if i use now() instead of manually typed dates the query take about 1400ms :(
> I thought the somebody posted to this list, that now() is a function that is not cached,
> and thatswhy does not work pretty well with indexes.
> I created a cached function cached_now() which returns now() but is declared with "isCacheable".
> If i use cached_now() instead of now the query takes also about 200ms :)
> Is it safe, or better could it have any side-effects, if i use my "own" cached_now() in such a query ?

I think you should use a high level language to wrap your PostgreSQL 
access (e.g. java, c, perl, ....).

Since you are gonna be running this query as a batch job,
you must use a high level lang that can handle dates in 
a UNIX-like way. (milisecs from 1970-01-01 00:00:00)

> 
> > > 
> > > [schnipp]
> > > 
> > 
> > -- 
> > ==================================================================
> > Achilleus Mantzios
> > S/W Engineer
> > IT dept
> > Dynacom Tankers Mngmt
> > Nikis 4, Glyfada
> > Athens 16610
> > Greece
> > tel:    +30-210-8981112
> > fax:    +30-210-8981877
> > email:  achill@matrix.gatewaynet.com
> >         mantzios@softlab.ece.ntua.gr
> > 
> > 
> > ---------------------------(end of broadcast)---------------------------
> > TIP 6: Have you searched our list archives?
> > 
> > http://archives.postgresql.org
> 

-- 
==================================================================
Achilleus Mantzios
S/W Engineer
IT dept
Dynacom Tankers Mngmt
Nikis 4, Glyfada
Athens 16610
Greece
tel:    +30-210-8981112
fax:    +30-210-8981877
email:  achill@matrix.gatewaynet.com
        mantzios@softlab.ece.ntua.gr