Buildfarm bug fix for MSVC builds

Unfortunately there was a small bug in yesterday's buildfarm client release. The bug only affects MSVC builds, which would fail silently on the HEAD (master) branch.

There is a bug fix release available at http://www.pgbuildfarm.org/downloads/releases/build-farm-4_15_1.tgz or you can just pick up the fixed version of run_build.pl (the only thing changed) at https://raw.githubusercontent.com/PGBuildFarm/client-code/b80efc68c35ef8a1ced37b57b3d19a98b8ae5dd2/run_build.pl

Sorry for the inconvenience.

New PostgreSQL Buildfarm Client Release

I have just released version 4.15 of the PostgreSQL Buildfarm Client. Here's what's changed:

• support the new location for pg_upgrade
• support running tests of client programs
• support building, installing and running testmodules
• use a default ccache directory
• improve logging when running pg_upgrade tests
• handle odd location of Python3 regression tests
• add timestamp to default log_line_prefix
• make qw() errors in the config file fatal (helps detect errors)
• minor bug fixes for web script settings.
• allow for using linked git directories in non-master branches

The last item might need a little explanation.  Essentially this can reduce quite dramatically the amount of space required if you are building on more than one branch. Instead of keeping, say, 6 checked out repos for the current six tested branches, we keep one and link all the others to it. This works almost exactly the way git-new-workdir does (I stole the logic from there). This doesn't work in a couple of situations: if you are using Windows or if you are using git-reference. In these cases the new setting is simply ignored.

To enable this new setting in an existing installation, do the following after installing the new release:

• in your config file, add this setting:
  git_use_workdirs => 1,
• remove the pgsql directory in each branch directory other than HEAD

Another good thing to do in existing installations would be to add "%m" to the beginning of the log_line_prefix setting in extra_config stanza.

Enjoy!

Hot Fix for buildfarm client, currently broken by pg_upgrade move

Yesterday the pg_upgrade program was moved from contrib to bin in the source tree. Unfortunately this broke most of those buildfarm members which check pg_upgrade. There is a hot fix for the TestUpgrade buildfarm module that can be downloaded from github. I will work on cutting a new buildfarm release in the next few days, but this file can just be dropped in place on existing installations.

Dynamically disabling triggers without locks

Recently Simon Riggs committed a patch by himself and Andreas Karlsson to reduce the lock strength required by certain ALTER TABLE commands, including those to enable or disable triggers. Now the lock level required is SHARE ROW EXCLUSIVE instead of ACCESS EXCLUSIVE. That means it doesn't block SELECT commands any more, and isn't blocked by them, although it will still block and be blocked by INSERT, UPDATE and DELETE operations. Very nice.

However, without formally disabling a trigger you can tell it dynamically not to do anything in the current session without taking any locks at all. Here's a little bit of PLpgsql code I wrote recently for this sort of operation in an INSERT trigger:

    begin
        disabled := current_setting('mypackage.foo_trigger_disabled');
    exception
        when others then disabled := 'false';
    end;
    if disabled = 'true' then
       return NEW;
    end if;

Note that this will only block the trigger from doing anything in sessions where this variable is set. But that's often exactly what you want. In the case this was written for, the trigger is redundant (and expensive) for certain bulk operations, but required for normal operations.  So in a session where we are performing the bulk operation, we can simply set this and avoid taking out a heavy lock on the table, and do this instead, before running our bulk operation:

    set mypackage.foo_trigger_disabled = 'true';

The code above is a bit ugly because of the requirement for the exception handler. There's a cure for that coming, too. David Christensen has submitted a patch to provide a form of current_setting() which will return NULL for unset variables instead of raising an exception.

Note, too, that you could use a value in a one-row one-column table if you wanted something that could apply in all sessions, not just the current session. It would be a bit less efficient, though. This mechanism is pretty light-weight.

Fun with Raspberry Pi 2 and the buildfarm

Here's a picture of my two Raspberry Pi 2 boxes, both running headless and wireless.

One is running Raspbian, installed via NOOBS, and the other Fidora, a remix of Fedora 21 for Raspberry Pi 2. It turned out that Pidora doesn't work on the Raspberry Pi 2, a fact that is extremely well hidden on the Raspberry Pi web site.

I have set up test buildfarm animals on both of these. But something odd is happening. They are both getting intermittent failures of the stats regression test. Sometimes it happens during "make check", sometimes during "make installcheck" and sometimes during testing of pg_upgrade (which in turn runs "make installcheck").

These machines are not anything like speed demons. Far from it. But we also run other slow machines without getting this happening all the time. So I'm a bit perplexed about what might be going on.

Incidentally, if you want to play with one of these, I do recommend getting a starter kit from Amazon or elsewhere. It's probably cheaper than buying everything separately, and gets you everything you need to get started. Well worth the $69.99.