Update takes longer than expected - Mailing list pgsql-general

From Andy Chambers
Subject Update takes longer than expected
Date
Msg-id CAAfW55pD3k291Sk3D7jGt-dUjOroSZLgm73htLf=vt+XvAtRRA@mail.gmail.com
Whole thread Raw
Responses Re: Update takes longer than expected  (Bill Moran <wmoran@potentialtech.com>)
Re: Update takes longer than expected  (Tom Lane <tgl@sss.pgh.pa.us>)
Re: Update takes longer than expected  (John R Pierce <pierce@hogranch.com>)
Re: Update takes longer than expected  (Jerry Sievers <gsievers19@comcast.net>)
List pgsql-general
Hi,

I have an update that takes longer than expected and wondered if
there's an easy way to make it go faster.

It's pretty simple:-

create table session (
  id serial primary key,
  data text);

update session
  set data = 'ipsum lorem...'
  where id = 5;

The "ipsum lorem.." stuff is an encrypted session variable from a
rails app that does tend to get quite large

select avg(length(data)) from session
=> 31275

We're trying to migrate the app from mysql to pg and this is one of
the performance bottle-necks.  Unfortunately it slows down every
request by about 5 seconds.  MySQL (both MyISAM and InnoDB) does this
almost instantaneously.

Cheers,
Andy

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