BUG #13637: ~2 GB psql import fails with out of memory error on machine with 64 GB RAM

The following bug has been logged on the website:

Bug reference:      13637
Logged by:          Aaron C. de Bruyn
Email address:      aaron@heyaaron.com
PostgreSQL version: 9.3.9
Operating system:   Ubuntu 14.04 x64
Description:

I have a small digital ocean virtual machine w/ 512 MB RAM running a small
Sentry database (http://getsentry.com) for error reporting as well as a few
'dev' databases for websites and applications being designed.

Unfortunately I wasn't running the sentry 'cleanup' script, and my sentry
database grew to approximately 2.3 GB (according to the nightly dump from
autopostgresqlbackup.

I was running 9.1.x and decided it was time to upgrade.  I upgraded to 9.3.
During the upgrade, a misunderstanding of the Ubuntu upgrade scripts caused
me to 'pg_dropcluster --stop 9.3 main' after the scripts had already
upgraded 9.1 to 9.3 on my behalf.

Time to restore databases from my nightly backups.  :)

All my databases restored except for the sentry database.

Running 'psql sentry < sentry.sql' as the postgres user shows tables being
created, rows being inserted, etc...

It runs for a few minutes, and then I either get an out of memory error, or
it appears to exit normally without importing the data.

Thinking it was because my 'dev' server is only 512 MB, I temporarily scaled
it up to 8 GB.  Same error.

I scaled it up to 16 GB.  Same error.

I went whole-hog and scaled it to 64 GB.
Same error.

I kept trying and discovered that the box never gets below ~54 GB free
meaning less than 10 GB are being used up when it reports being out of
memory

I rebooted out of frustration, I tweaked sysctl settings for overcommitting
memory, etc...

No effect.

Finally I removed all the tweaks, scaled the box back to 512 MB, and
rebooted to start gathering info for a bug report.

I started running 'psql sentry < sentry.sql' and was watching the memory
usage drop when I noticed that I had forgotten to re-create my swap file
after the last reboot.

I ran swapon and watched as psql kept running while never touching my
swapfile, and my box continued to hover around 150K free.

By the time it crashed with an out-of-memory error, it restored most of the
tables in the database.

I tried importing again with the swap file in-place, and it consumed all the
memory and crashed.  I tried disabling swap, starting psql, then enabling
swap and I was able to restore the same majority of tables.

I'm sorry I can't pin this down further, but it's a bit out of my depth at
this point.

I do have the ~2.3 GB backup of the DB which bzip's down to ~550 MB if any
developers are interested in playing/testing.