Re: Merge David and Goliath tables efficiently - Mailing list pgsql-performance

From nicolas paris
Subject Re: Merge David and Goliath tables efficiently
Date
Msg-id dc4115489cd1bbddab1fea3cf0eeb8bdd06657e7.camel@riseup.net
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In response to Re: Merge David and Goliath tables efficiently  (Tomas Vondra <tomas.vondra@enterprisedb.com>)
Responses Re: Merge David and Goliath tables efficiently  (Tomas Vondra <tomas.vondra@enterprisedb.com>)
List pgsql-performance
> IMHO the thing that breaks it is the ORDER BY in the merge, which
> likely
> acts as an optimization fence and prevents all sorts of smart things
> including the partitionwise join. I'd bet that if Nicolas replaces
>
>   MERGE INTO "goliath" ca
>   USING (SELECT * FROM "david" ORDER BY "list_id") AS t
>   .

Sorry if it was not clear, however there is no order by in the 2.1
strategy. Then this cannot be the reason of not triggering the optim.

For information I do enable partition join feature with jdbc call just
before the merge:
set enable_partitionwise_join=true



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