On 23/10/14 17:49, Pierre-Adrien Coustillas wrote:

Hello, (google translate) hi, (no google translate)

Aside turning the pipes on/off it would require significant programming expertise to play around with the internals of some of the optimizer modules. Best is to first understand where you encounter performance problems by studying the TRACE command, possibly followed by using the stethoscope and tomograph. regards, Martin [1]https://www.monetdb.org/Documentation/Manuals/SQLreference/Trace [2] https://www.monetdb.org/Documentation/Manuals/MonetDB/Profiler/Stethoscope [3] https://www.monetdb.org/Documentation/Manuals/MonetDB/Profiler/tomograph

I am a little fun with the optimizer.

sql>select count(distinct idvisiteur) from src_inbox__at__lm__visites; + ---------- + | L1 | + + ========== | 75528080 | + ---------- + 1 tuple *(3m 51s) *

sql>set optimizer = 'minimal_pipe;

sql>select count (distinct idvisiteur) from src_inbox__at__lm__visites; + ---------- + | L1 | + + ========== | 75528080 | + ---------- + 1 tuple *(1m 28s) *

sql>set optimizer = 'default_pipe;

sql>select count (distinct idvisiteur) from src_inbox__at__lm__visites; + ---------- + | L1 | + + ========== | 75528080 | + ---------- + 1 tuple *(3m 54s) *

It's very interesting. Is there a risk to change optimizer ? What are the best practices ?

thank you

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