Re: [HACKERS] SendRowDescriptionMessage() is slow for queries with alot of columns

Hi Thom,

Thanks for taking a whack at this!

On 2017-09-15 12:16:22 +0100, Thom Brown wrote:
> I've run a fairly basic test with a table with 101 columns, selecting
> a single row from the table and I get the following results:
> 
> 
> Columns with 1-character names:
> 
> master (80 jobs, 80 connections, 60 seconds):

FWIW, I don't think it's useful to test this with a lot of concurrency -
at that point you're likely saturating the machine with context switches
etc. unless you have a lot of cores. As this is isn't related to
concurrency I'd rather just check a single connection.


> transaction type: /tmp/test.sql
> scaling factor: 1
> query mode: simple

I think you'd need to use prepared statements / -M prepared to see
benefits - when parsing statements for every execution the bottleneck is
elsewhere (hello O(#available_columns * #selected_columns) in
colNameToVar()).

Greetings,

Andres Freund


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