Daily Archives: November 2, 2011

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November 2, 2011

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Systems (Administration)

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Saving your workspace window configuration in Linux [1102]

I am usually working on a good half a dozen things at any given time and this means that I usually have a good ten or twenty windows open. My chromium currently has a 134 tabs and this is after I  cleaned up and closed all the tabs I no longer need.

Luckily, working in Linux means that I can spread each stream of work into the various workspaces.

Now GNOME 3 makes things a little more complicated with the dynamic workspaces but I’m learning to use it to my advantage

However, with Ubuntu 11.10 Oneiric Ocelot and GNOME 3, I seem to be running into an issue regularly…If I leave my computer for a while, it doesn’t unlock correctly. The screen remains black and I can’t move the mouse to my second screen and the unlock screen doesn’t show up.

Thinking about it, it seems like there might be two screen savers being started but I shall investigate that tomorrow. I have the same issue at both work and home so it is more likely to be related to Ubuntu + GNOME 3 or something about the way I set things up.

I  usually resolve this by logging into the console and here a neat trick for killing all our processes in one fell swoop.

$ kill -9 -1

Another thing I have been doing a bit more of recently is gaming which involves rebooting in Windows.

Both of the above leaves me with a restarted workspace. Starting up the applications pops them all into the same workspace. Chrome is especially a nightmare. I might have 135 open tabs but they are in about 6 windows spread across four workspaces.

It is annoying to have to distribute these things out each time.

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November 2, 2011

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Database Systems

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Tracking progress of an update statement [1101]

Sometimes there is a need to execute a long running update statement. This update statement might be modifying millions of rows as was the case when we went hunting for a way to track the progress of the update. Hunting around took us to http://archives.postgresql.org/pgsql-admin/2002-07/msg00286.php In our particular case, we are using postgresql but this should work with any database server that provides sequences. Our original sql was of the form:

update only table1 t1
set amount = t2.price
from table2 t2
where t1.id = t2.id;

There is of course now way of figuring out how many rows had been updated already. The first step was to create a sequence

CREATE TEMPORARY SEQUENCE seq_progress START 1;

We can then use this sequence in the update statement to ensure that each row updated also increments the sequence

update only table1 t1
set amount = t2.price
from table2 t2
where nextval('seq_progress') != 0
and t1.id = t2.id;

Once the query is running, you can open another connection to the database. To get an indication of how far it has got, you can just run the following

 select nextval('seq_progress');

Bear in mind that this will also increment it by 1 but if you have millions of rows which is really the only case in which this would be useful, a few additional increments is hardly going to make a difference.

Good luck and have fun!