Date: Tue, 4 Dec 2018 06:44:18 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Surafel Temesgen <surafel3000@gmail.com>,
	Adam Berlin <berlin.ab@gmail.com>,
	pgsql-hackers@lists.postgresql.org
Subject: Re: COPY FROM WHEN condition
Message-ID: <20181204094418.wpr6mxrtsuxb5mlq@alvherre.pgsql>
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After reading this thread, I think I like WHERE better than FILTER.
Tally:

WHERE: Adam Berlin, Lim Myungkyu, Dean Rasheed, yours truly
FILTER: Tomas Vondra, Surafel Temesgen

Couldn't find others expressing an opinion in this regard.

On 2018-Nov-30, Tomas Vondra wrote:

> I think it should be enough just to switch to CIM_SINGLE and increment the
> command counter after each inserted row.

Do we apply command counter increment per row with some other COPY
option?  Per-row CCI makes me a bit uncomfortable because with you'd get
in trouble with a large copy.  I think it's particularly nasty here,
precisely because you may want to filter out some rows of a very large
file, and the CCI may prevent that from working.
I'm not convinced by the example case of reading how many tuples you've
imported so far in the WHERE/WHEN/FILTER clause each time (that'd become
incrementally slower as it progresses).

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services