Resolve the "Unserialize" error on Drupal and PostgreSQL

If you are working with Drupal and PostgreSQL, this is probably not the first time you encountered some weird compatibility issues, but this one is pretty twisted.

It happened to me after having restored a database dump and trying to access the homepage of my website, I kept getting hit by “Notice: unserialize() [function.unserialize]: Error at offset[…]” messages that occured multiple times during Drupal’s boostraping process and ultimatly shutting down with fatal errors on common core functions like user_access() that couldn’t be found. I couldn’t even run the update.php script!

After scouring the Google for answers and following guides after guides adressing this very issue, it turned out that the culprit was the new version of PostgreSQL. Starting with 9.0, it introduced a new “hex” format for bytea type output, which doesn’t do too well with Drupal who’s apparently expecting the good ol’ “escape” format.

So the solution for this is just to set the database’s bytea_output format to escape:

ALTER DATABASE yourdb SET bytea_output='escape'; 

After that just clear your cache with:

drush cc all

And you should be good to go!