On 5/10/2012 1:10 PM, Lee Hachadoorian wrote:
> Does anyone have experience or advice on how to efficiently issue a
> large number of COPY statements? The data (US Census) comes in> 100
> "segments" (each will be copied to its own database tables) for each
> state (51), for a total of> 5000 text files. I can generate the COPY
> statements with a script.
>
> The two specific question I can think of (but I'm sure there's more
> that I'm not thinking of) are:
>
> 1) "COPY is fastest when used within the same transaction as an
> earlier CREATE TABLE or TRUNCATE command. In such cases no WAL needs
> to be written, because in case of an error, the files containing the
> newly loaded data will be removed anyway." Would I be able to take
> advantage of this if I:
>
> BEGIN;
> TRUNCATE import_table;
> COPY import_table FROM 'file1';
> COPY import_table FROM 'file2';
> ...
> COPY import_table FROM 'file51';
> END;
Yes, I believe so.
>
> 2) Is there a performance hit to doing a COPY to more than one table
> in the same transaction?
No, I don't think so. I assume you are the only user hitting the
import_table, so holding one big transaction wont hurt anything.
>
> Any other advice will be appreciated.
To really speed it up, you'd need to run multiple concurrent connections
each doing COPY's. Maybe up to the number of cores you have. (of
course you dont want each connection to fire off truncates, but
concurrent should trump "skip wall" in terms of speed).
If import_table is just a temp holding stot you can look into temp
and/or unlogged tables.
-Andy