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>include sql;
# MonetDB/SQL module v2.35.0 loaded
[New Thread 0x7fffe4f37710 (LWP 24664)]
>sql.start();
>select not(invalidtable.bla) from tables;
Program received signal SIGSEGV, Segmentation fault.
0x00007fffe540aa4f in exp_subtype (e=0x0) at ../../../src/server/rel_exp.mx:446
446 switch(e->type) {
(gdb) bt
#0 0x00007fffe540aa4f in exp_subtype (e=0x0) at...
2010-01-06 21:21:40 UTC in MonetDB
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It currently does do a cost assessment in exp_count(int *cnt, int seqnr, sql_exp *e), sql/src/server/rel_optimizer.mx. Is it there where a preference is set for the like operation?
Never the less, I do see your point regarding (user-defined) functions, what I do not understand is that the actual operations are also (user defined) function, for them a cost is set. It seems that the long term...
2010-01-05 12:53:27 UTC in MonetDB
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If I shutdown my MonetDB public server, that would probably give a performance increase as well. Anything else in the New Year, Fabian?.
2010-01-05 11:50:05 UTC in MonetDB
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It seems in a query like:
explain select kvk from kvk where length('hello') = length(bedrijfsnaam) and bedrijfsnaam like '%hello%';
The like operation is before the length, I have attached the mal explain of it. This is the plan:
project (
| select (
| | table(sys.kvk) [ kvk.kvk, kvk.bedrijfsnaam, kvk.%TID% NOT NULL ]
| ) [ length(kvk.bedrijfsnaam) = length('hello')...
2010-01-05 11:45:25 UTC in MonetDB
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In a query: select * from x where a like '%%'; it is obvious to see that this query could be rewritten to select * from x; The calculation of this like expression obviously takes time. The negative case might look even more fruitful, since it can prevent an entire query from running.
2010-01-05 11:35:46 UTC in MonetDB
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When the IN operator is applied on a column and the column has a zero count, the (..) does not have to be executed.
The same goes Update and Delete.
2009-12-26 10:00:05 UTC in MonetDB
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sql>select (4.4054292 - 4.40572025343667)^2;
+------------------------+
| sql_sub_single_value |
+========================+
| 8.4712102997417702e-08 |
+------------------------+
1 tuple
sql>select (52.0903881 - 52.091375762174)^2;
+------------------------+
| sql_sub_single_value |
+========================+
| 9.7547656995040638e-07 |
+------------------------+
1 tuple...
2009-12-26 05:01:32 UTC in MonetDB
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;)
Other database support 'dynamic' DEFAULTs. Hence you are allowed to place an expression into the default. This is currently not possible in MonetDB where it is static.
I don't see the big problem (performance) problem in this as long the default is added on the end of a bulk transaction. Instead of foreach record. S in general it would be an 'on-insert-update-trigger', opposed to the...
2009-12-01 09:44:12 UTC in MonetDB
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This one is on the count, and is partly implemented. The example above here works. The other one is that the sum of the cross product equals the sum of one multiplied by the amount of joins to come to the cross product itself.
So count(*)^N vs sum(something)*N.
2009-12-01 09:01:55 UTC in MonetDB
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What is written in the summary is. But since there was one rewrite option left I didn't close it.
2009-12-01 08:56:11 UTC in MonetDB
