Re: [Monetdb-developers] Single column select vs aggregation

18 Feb 2010


      Op 18-02-10 18:23, Stefan Manegold schreef:
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On Thu, Feb 18, 2010 at 05:46:31PM +0100, Stefan de Konink wrote:
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Attached is a trace of a single column select operation, with a max,
avg and equality.
The equality takes about 4 times more time than the avg operation.
From the plan I see that the operation is executed paralel, but I do
wonder why suddenly the uselect takes such a high amount of time.
Which version of MonetDB?
CVS HEAD, 2 am.
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How configured / compiled?
--enable-assert --enable-debug
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How was the mserver5 started (which command line options were given)?
/opt/monetdb-head/bin/mserver5 --dbfarm=/home/skinkie/monetb 
--dbname=kvk --dbinit="include sphinx; include sql;" --set mapi_port=50001
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Any changes compared to the default monetdb5.conf?
No, not changed anything in there.
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Is the "kvk" column sorted?
No, it does include a partial sort (msb are sorted). A 32bit column 
(kvks) that is (or either should be...) ends up with between 170ms ~ 220ms.
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Could you run the select query in the MAL debugger
(DEBUG select kvk from kvk where kvk = 412657690010;),
single step through it,
set the debug mask to 2097152
(debug 2097152)
just before the algebra.uselect() is executed,
and report the output on the server console after the algebra.uselect() has
been executed?
Do you mean this?

mdb>#    _44 := 
algebra.uselect(_40=:bat[:oid,:lng][1196532],A0=412657690010:lng);
mdb>
#BAT_select_(b=tmp_5710): sampling: tmp1 = BATslice(b=tmp_5710, 
_lo=598266, _hi=598371);
#BAT_select_(b=tmp_5710): sampling: tmp2 = BAT_select_(tmp1=tmp_5704, 
tl, th, tail);
#BAT_select_(b=tmp_5704): BAT_scanselect(b=tmp_5704, bn=tmp_5703, tl, 
th, equi=1, nequi=0, lval=1, hval=1, nocheck=1);
#seqscan_eq_lng_void_tloc_oid_vid_nocheck_noinc[if ( simple_EQ(tl 
,v,lng)                      ),v,oid_ctr,oid_ctr++;](b=tmp_5704, 
bn=tmp_5703, tl, th, oid_ctr=598266, str_idx=0);
#BAT_select_(b=tmp_5704): tmp_5703: hkey=1, tkey=0, 
hsorted=139659451564097, tsorted=0.
#BAT_select_(b=tmp_5710): BAT_hashselect(b=tmp_5710, bn=tmp_5703, tl); 
(building hash-table on the fly)
#BAThash: create hash(1196532);
#BAT_select_(b=tmp_5710): tmp_5703: hkey=1, tkey=0, 
hsorted=139659451564032, tsorted=139659451564032.


Stefan