Adding column to Postgres table fails I have a Postgres (8.4.20) table that I'm supposed to add columns to, but it seems to have some problems that I have difficulties to debug:

I'm attempting what I thought was a simple ALTER TABLE... on it:

db_name=&gt; ALTER TABLE "marking" ADD COLUMN published TIMESTAMP WITHOUT TIME ZONE;
ERROR:  canceling statement due to statement timeout


I'm puzzled, because:


Although the table has (very little) data in it, it's not a NOT NULL column
I've also tried to dump the table, delete it's contents and re-run without data in it


But it still gives the same result. Here's the current schema for the table:

db_name=&gt; \d marking
           Table "public.marking"
 Column |         Type          | Modifiers
--------+-----------------------+-----------
 link   | character varying(32) | not null
 hash   | character varying(40) | not null
 url    | text                  | not null
 blob   | text                  | not null
Indexes:
    "marking_pkey" PRIMARY KEY, btree (hash)
    "ix_marking_link" btree (link)


Sorry for the newbie question, but there's clearly something fundamental I don't understand here and I'm having some trouble getting further.

I've tried to increase statement_timeout and work_mem, but even very large values won't help.
The alter table was probably waiting to get an exclusive lock on the table. If you have transactions touching the table, the ALTER TABLE will wait until all those transactions are committed 

You can check if your statement is waiting for such a lock by looking at pg_stat_activity and pg_locks. 

If you have sessions that are shown as idle in transaction those are a potential cause for that.



Unrelated, but: Postgres 8.4 is no longer supported (=maintained). You should plan your upgrade to a supported version (9.3 or 9.4) as soon as possible. If you have to stick with 8.4 you should at least be running the latest 8.4 version which is 8.4.22