Hi, group. subgroupdone (X_169,X_248); it the grouping on the last of your three group by columns (well, last means the last one MonetDB calculates, but MonetDB does not necessarily calculate the groupings in the order you specify). prefixing you query with TRACE (as well as the stethoscope output) should tell you also how large the intermediate results are; in general grouping is a complex (and thus possibly expensive) operation ... Best, Stefan ----- Original Message -----

Hi,

I try to analyze the slowness of a query with EXPLAIN and stethoscope

The query is : SELECT count (*) FROM ( SELECT id_unique, siteniveau1, siteniveau2, '0000-00-00', 0, 0, MAX( debutvisite ), 0, 0 FROM tmp __ at __ lm __visites_ agregees _id_unique GROUP BY id_unique,siteniveau1,siteniveau2 ) tbl ;

the beginning of explain is ( there is 272 tuples ) +============================================================================================================================================================================================+ | function user.s2_5{ autoCommit = true }(A0: str ,A1: bte ,A2: bte ,A3: bte | ,A4: bte ): void ; | | barrier X_429 := language . dataflow (); | | X_7 := sql . mvc (); | | X_55:bat[: oid ,: oid ] := sql . tid (X_7," sys "," tmp __ at __ lm | __visites_ agregees _id_unique",0,8); | | X_70:bat[: oid ,: int ] := sql . bind (X_7," sys "," tmp __ at __ lm | __visites_ agregees _id_unique","id_unique",0,0,8); | | (X_78:bat[: oid ,: oid ] ,X_79:bat[: oid ,: int ] ) := sql . bind (X_7," | sys "," tmp __ at __ lm __visites_ agregees | _id_unique","id_unique",2,0,8); | | X_161 := sql .delta(X_70,X_78,X_79); | | X_169 := algebra . leftfetchjoin (X_55,X_161); | | X_96:bat[: oid ,: int ] := sql . bind (X_7," sys "," tmp __ at __ lm | __visites_ agregees _id_unique","siteniveau1",0,0,8); | | (X_111:bat[: oid ,: oid ] ,X_112:bat[: oid ,: int ] ) := sql . bind (X_7," | sys "," tmp __ at __ lm __visites_ agregees | _id_unique","siteniveau1",2,0,8); | | X_184 := sql .delta(X_96,X_111,X_112); | | X_193 := algebra . leftfetchjoin (X_55,X_184); | | X_129:bat[: oid ,: int ] := sql . bind (X_7," sys "," tmp __ at __ lm | __visites_ agregees _id_unique","siteniveau2",0,0,8); | | (X_144:bat[: oid ,: oid ] ,X_145:bat[: oid ,: int ] ) := sql . bind (X_7," | sys "," tmp __ at __ lm __visites_ agregees | _id_unique","siteniveau2",2,0,8); | | X_201 := sql .delta(X_129,X_144,X_145); | | X_209 := algebra . leftfetchjoin (X_55,X_201); | | (X_224,X_225,X_226) := group. subgroup (X_209); | | (X_248,X_249,X_250) := group. subgroup (X_193,X_224); | | (X_272,X_273,X_274) := group. subgroupdone (X_169,X_248); | | X_275 := algebra . leftfetchjoin (X_273,X_169); | | X_304 := algebra . leftfetchjoin (X_273,X_248); | | X_331 := algebra . leftfetchjoin (X_304,X_249);

group. subgroupdone (X_169,X_248); set 10 minutes to run . Why ? how to understand this function ?

Thank

Pierre

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