why cql query long time

Question

My query:

cqlsh:mynap_db> select complete_row from tbl_rowsxml_map  where cache_type_name='IncomingCache' and user_id ='34014'  limit 1 ALLOW FILTERING;

 complete_row
--------------

(0 rows)

If it returns 0 rows then why does it take such a long time to execute?

Please help me to understand the reason.

How many rows are there in your table tbl_rowsxml_map? – PVR Sep 01 '16 at 06:47 — PVR, Sep 01 '16 at 06:47

score 4 · Answer 1 · edited May 23 '17 at 10:30

4

ALLOW FILTERING is a reason. That means that your schema not allowing you to run this query effectively, so, you allowing Cassandra itself to select much more data from every node and filter data after. Usually is a quite non-effective operation.

Check Datastax' explanation for details or this answer.

edited May 23 '17 at 10:30

Community

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answered Sep 01 '16 at 08:06

deniszh

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Agree. ALLOW FILTERING is the root of all evil. – Aaron Sep 01 '16 at 13:37

why cql query long time

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