Month: October 2014

PostgreSQL + Perl + Unicode == confusion. Why?

Yesterday I had an interesting discussion on irc.

A guy wanted to know why Perl script is causing problems when dealing with Pg
and unicode characters.

The discussion went sideways, I got (a bit) upset, and had to leave anyway, so
I didn't finish it. But it did bother me, as for me the reasons of the problem
seem obvious, yet the person I talked with was very adamant that I have the
whole thing wrong.

So, I figured I'll use my blog to elaborate a bit…

Continue reading PostgreSQL + Perl + Unicode == confusion. Why?

What logging has least overhead?

When working with PostgreSQL you generally want to get information about slow queries. The usual approach is to set log_min_duration_statement to some low(ish) value, run your app, and then analyze logs.

But you can log to many places – flat file, flat file on another disk, local syslog, remote syslog. And – perhaps, instead of log_min_duration_statement – just use pg_stat_statements?

Well, I wondered about it, and decided to test.

Continue reading What logging has least overhead?

Waiting for 9.5 – Implement SKIP LOCKED for row-level locks

On 7th of October, Alvaro Herrera committed patch:

Implement SKIP LOCKED for row-level locks
 
This clause changes the behavior of SELECT locking clauses in the
presence of locked rows: instead of causing a process to block waiting
for the locks held by other processes (or raise an error, with NOWAIT),
SKIP LOCKED makes the new reader skip over such rows.  While this is not
appropriate behavior for general purposes, there are some cases in which
it is useful, such as queue-like tables.
 
Catalog version bumped because this patch changes the representation of
stored rules.
 
Reviewed by Craig Ringer (based on a previous attempt at an
implementation by Simon Riggs, who also provided input on the syntax
used in the current patch), David Rowley, and Álvaro Herrera.
 
Author: Thomas Munro

Continue reading Waiting for 9.5 – Implement SKIP LOCKED for row-level locks

Waiting for 9.5 – Row-Level Security Policies (RLS)

On 19th of September, Stephen Frost committed patch:

Row-Level Security Policies (RLS)
 
Building on the updatable security-barrier views work, add the
ability to define policies on tables to limit the set of rows
which are returned from a query and which are allowed to be added
to a table.  Expressions defined by the policy for filtering are
added to the security barrier quals of the query, while expressions
defined to check records being added to a table are added to the
with-check options of the query.
 
New top-level commands are CREATE/ALTER/DROP POLICY and are
controlled by the table owner.  Row Security is able to be enabled
and disabled by the owner on a per-table basis using
ALTER TABLE .. ENABLE/DISABLE ROW SECURITY.
 
Per discussion, ROW SECURITY is disabled on tables by default and
must be enabled for policies on the table to be used.  If no
policies exist on a table with ROW SECURITY enabled, a default-deny
policy is used and no records will be visible.
 
By default, row security is applied at all times except for the
table owner and the superuser.  A new GUC, row_security, is added
which can be set to ON, OFF, or FORCE.  When set to FORCE, row
security will be applied even for the table owner and superusers.
When set to OFF, row security will be disabled when allowed and an
error will be thrown if the user does not have rights to bypass row
security.
 
Per discussion, pg_dump sets row_security = OFF by default to ensure
that exports and backups will have all data in the table or will
error if there are insufficient privileges to bypass row security.
A new option has been added to pg_dump, --enable-row-security, to
ask pg_dump to export with row security enabled.
 
A new role capability, BYPASSRLS, which can only be set by the
superuser, is added to allow other users to be able to bypass row
security using row_security = OFF.
 
Many thanks to the various individuals who have helped with the
design, particularly Robert Haas for his feedback.
 
Authors include Craig Ringer, KaiGai Kohei, Adam Brightwell, Dean
Rasheed, with additional changes and rework by me.
 
Reviewers have included all of the above, Greg Smith,
Jeff McCormick, and Robert Haas.

Continue reading Waiting for 9.5 – Row-Level Security Policies (RLS)