I'm running a command to create a new column on a fairly large table (about 315 million rows). This used more disk space than I expected and it has completely filled up my SAN. The command failed with the
ERROR: could not extend file "pg_tblspc/14342 etc.": No space left on device
My questions are, when a command fails like this, are the results of the command not immediately discarded? Why when no actual changes have been made to the table, is the tablespace still full?
And finally, what is the best way to free up space again when postgres will not allow to me execute any other commands e.g. VACUUM?