Monday, February 6, 2017

Module Monday: safeupdate

A recent tweet pointed me to safeupdate which is a little extension that forbids unconditional UPDATE and DELETE statements, i.e. without WHERE clause.

Let's see how this works...

The build and install procedure is pretty non-spectacular: make, make install and then either activate it per session with load 'safeupdate' or globally by adding it to postgresql.conf:

shared_preload_libraries = 'safeupdate'

After that, if you try an unconditional UPDATE or DELETE on any table, you'll get the following errors:

ERROR:  UPDATE requires a WHERE clause


ERROR:  DELETE requires a WHERE clause

respectively and the operation is cancelled.

Unconditional UPDATE and DELETE can still be forced by using a condition that always evaluates to true, like


But now you have to explicitly request this behaviour.

I think this is ever so useful to protect against human error, that I wonder why this isn't something mandatory, even if it's non-standard.

However, there is one glitch: If you JOIN tables to UPDATE or DELETE only certain rows that match the ON condition, this is not recognized as a conditional operation and the WHERE TRUE is still needed to pacify the extension. Well, I can live with that...

Monday, January 23, 2017

A new type for PostgreSQL

CREATE TYPE trumpean AS ENUM ('true', 'alternateTrue');

Wednesday, January 4, 2017

What happened?

Vereinigte Staaten
Tschechische Republik
Vereinigtes K├Ânigreich

Germany suddenly jumped from a two-digit to a four-digit access count?

Sudden FAME! ;-)

Friday, December 30, 2016

One-time passwords with Google Authenticator PAM (and friends)

PostgreSQL allows for more than plain password authentication in pg_hba.conf. One of the most flexible is authenticating against a PAM.

Let's see how this works with one-time passwords from  Google Authenticator.

1.) Install Google Authenticator on your Android or iOS device.

2.) Install the Google Authenticator PAM on the machine where your PostgreSQL server lives, like in Step 1 - 4 of this guide.

3.) Connect your device with the account on that machine.

4.) Create a login role for the database but without a password. Since roles without password can never log in regularly (See the PASSWORD remarks here), this limits this role to PAM logins.

5.) Configure a PAM service for PostgreSQL. E.g. create a file named postgresql where your PAM configs live, on Ubuntu this is /etc/pam.d/. The file should look like this:

auth         sufficient

6.) Configure PostgreSQL to use the PAM. E.g. a line in pg_hba.conf could look like this:

hostssl    all    all   pam    pamservice=postgresql

And that's basically it. Now, next time you login, PostgreSQL will ask you for a password that is generated individually on your device.

Of course you can use all kinds of PAM with PostgreSQL like this.

Unfortunately, I also found a few caveats along the way. :-(

First, PostgreSQL clients will ask only for one password, regardless if you chain n PAM's for n-factor authentication.

So if you e.g. chain a PAM against LDAP with Google Authenticator as the second factor, this won't work. This seems to be a shortcoming of the PAM implementation in PostgreSQL, not expecting multiple password prompts. It is still possible to enable n-factor authentication though, but only one PAM can prompt for a password. If the other factors are hardware devices like a fingerprint scanner that does not prompt for a password, you are fine.

Alternatively, you can provide your own PAM that takes all passwords in one prompt and handles them internally.

Second, PAM requires PostgreSQL clients to send the password in plaintext. So now is the time to switch on TLS and make it mandatory (Noticed the hostssl switch above?).

Third, some clients like pgAdmin3 break with one-time passwords, because they apparently open new connections without prompting for a password again, but re-use the initial one instead until you disconnect. This obviously does not work with passwords which are valid only for one login attempt.

Wednesday, November 30, 2016

Stampede is out!

Stampede just got live!

I'll try this for sure, when I have time, when I have time...

Sunday, November 27, 2016

pgchem::tigress 4.0 released

pgchem::tigress 4.0 is finally out!
  • This builds against PostgreSQL >= 9.4.x and OpenBabel 4.2.x on Linux.
  • It contains all fixes and contributions of the previous versions.
  • Support for building with Indigo has been removed
  • A lot of dead code has been removed
  • All palloc calls have been replaced by palloc0
  • MOLECULE is not binary compatible and needs to be recreated when you upgrade from 3.2 to 4.0!
  • MS spectrum creation has been removed. You may use enviPat instead for much more accurate spectra 
So: CREATE EXTENSION pgchem_tigress;

Friday, November 18, 2016

tcn again

In the previous post, I suggested that contrib/tcn for example could be used to selectively update caches.

OK, here is my try:

By touching the cache only when the database signals a change of the base table and using the passed information to touch the affected rows only, this should be much more efficient than other strategies like routinely invalidating the cache every n minutes or so.