Many thx for the explanation Aaron.
On Wednesday, July 4, 2012, aaron morton wrote: > > select my_cf where columnA = a and columnB = b and columnC = c and > columnD = d > Cassandra will only use one equality clause to select the candidate rows. > The other clauses are applied to the rows using that first clause. > > The clause to use to select candidate rows is based on statistics that > estimate the number of columns in the indexes. > > > Do you have any ideas? is there any way to understand how cassandra > internally run the query (a kind of "explain plan")? > The only way I know of to see the "query plan" is to set DEBUG logging on > org.apache.cassandra.db.index.keys.KeysSearcher and look for the message > "Primary scan clause is " > > Note, if this is a common query you may get better performance creating a > custom secondary index than using four equality clauses in an index scan. > > > 2/ Is there any limitations on the number of criterias we can usually > have? > > None that I know of. Query will probably run slower the more you have. > > > 3/ Even if we have different data type (date, string, int), we have all > stored them as UTF8Type. Could we expect performance improvements if we use > DateType, LongType? > No. The main issue is going to be the selectivity of the primary scan > clause, followed by the number of additional clauses. Their types will have > very little / no impact. > > Hope that helps. > > ----------------- > Aaron Morton > Freelance Developer > @aaronmorton > http://www.thelastpickle.com > > On 3/07/2012, at 3:59 AM, Olivier Mallassi wrote: > > > Hi all > > > > We have 4 indexed columns; all configured in UT8Type even if one columns > is a date and the other an integer). > > > > 1/ the read query we run can have up to 4 criteria > > select my_cf where columnA = a and columnB = b and columnC = c and > columnD = d > > > > This query, is fast (<500ms) up to 3 criterias but when we add the > fourth one, the exection time is 9,5s. > > Do you have any ideas? is there any way to understand how cassandra > internally run the query (a kind of "explain plan")? > > > > 2/ Is there any limitations on the number of criterias we can usually > have? > > > > 3/ Even if we have different data type (date, string, int), we have all > stored them as UTF8Type. Could we expect performance improvements if we use > DateType, LongType? > > > > Many thx for all your answers. > > > > -- > > ............................................................ > > Olivier Mallassi > > OCTO Technology > > ............................................................ > > 50, Avenue des Champs-Elysées > > 75008 Paris > > > > Mobile: (33) 6 28 70 26 61 > > Tél: (33) 1 58 56 10 00 > > Fax: (33) 1 58 56 10 01 > > > > http://www.octo.com > > Octo Talks! http://blog.octo.com > > > > > > -- ............................................................ Olivier Mallassi OCTO Technology ............................................................ 50, Avenue des Champs-Elysées 75008 Paris Mobile: (33) 6 28 70 26 61 Tél: (33) 1 58 56 10 00 Fax: (33) 1 58 56 10 01 http://www.octo.com Octo Talks! http://blog.octo.com
