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How to migrate a Homebrew-installed PostgreSQL database to a new major version (9.3 to 9.4) on OS X

This guide assumes that you recently run brew upgrade postgresql and discovered to your dismay that you accidentally bumped from one major version to another: say 9.3.x to 9.4.x. Yes, that is a major version bump in PG land.

First let's check something.

brew info postgresql

The top of what gets printed as a result is the most important:

postgresql: stable 9.4.1 (bottled)
Conflicts with: postgres-xc
/usr/local/Cellar/postgresql/9.3.2 (2924 files, 39M)
  Poured from bottle
/usr/local/Cellar/postgresql/9.4.1 (2996 files, 40M) *
  Poured from bottle

The interesting bit is that there are two versions installed on my systems. Homebrew thankfully installs the Postgres binaries in different subfolders, which is very important to be able to migrate data from one version to the other.

As you can see I have my old version installed in /usr/local/Cellar/postgresql/9.3.2. The new version is in /usr/local/Cellar/postgresql/9.4.1.

First ensure that you have the correct PG binaries running:

which psql

psql --version
psql (PostgreSQL) 9.4.1

This means that the pg_upgrade binary we'll be using is also the new one. But let's not assume:

pg_upgrade --version
pg_upgrade (PostgreSQL) 9.4.1

Good good.

Mise en place

The directory where your actual database data is stored is different from the one where your PostgreSQL binaries are installed. Homebrew installs the data directory in /usr/local/var/postgres/ and doesn't touch that data folder when you upgrade from one version to the next. This is a good thing because if Homebrew tried to install a brand new database (with initdb) it could squash all your existing data.

First I recommend moving your existing data to a directory with a different name:

mv /usr/local/var/postgres/ /usr/local/var/postgres.9.3.backup/

Now that the old data directory has been "moved", you can safely create a brand new clean database:

initdb /usr/local/var/postgres/
The files belonging to this database system will be owned by user "olivierlacan".
This user must also own the server process.

The database cluster will be initialized with locale "en_US.UTF-8".
The default database encoding has accordingly been set to "UTF8".
The default text search configuration will be set to "english".

Data page checksums are disabled.

creating directory /usr/local/var/postgres ... ok
creating subdirectories ... ok
selecting default max_connections ... 100
selecting default shared_buffers ... 128MB
selecting dynamic shared memory implementation ... posix
creating configuration files ... ok
creating template1 database in /usr/local/var/postgres/base/1 ... ok
initializing pg_authid ... ok
initializing dependencies ... ok
creating system views ... ok
loading system objects' descriptions ... ok
creating collations ... ok
creating conversions ... ok
creating dictionaries ... ok
setting privileges on built-in objects ... ok
creating information schema ... ok
loading PL/pgSQL server-side language ... ok
vacuuming database template1 ... ok
copying template1 to template0 ... ok
copying template1 to postgres ... ok
syncing data to disk ... ok

WARNING: enabling "trust" authentication for local connections
You can change this by editing pg_hba.conf or using the option -A, or
--auth-local and --auth-host, the next time you run initdb.

Success. You can now start the database server using:

    postgres -D /usr/local/var/postgres
    pg_ctl -D /usr/local/var/postgres -l logfile start

Your output will be slightly different. For one, the user won't be olivierlacan but whatever your system user is. You can find that out easily with whoami.

Interesting to note, but if you use PostgreSQL with Rails. This means there will be no password on your development database, so you can skip the password field in database.yml or leave it *completely empty.


Let's get to it.

First we have to make sure both database servers are not running when we do the upgrade:

pg_ctl -D /usr/local/var/postgres stop -m fast
pg_ctl -D /usr/local/var/postgres.9.3.backup stop -m fast 

If you get the following message it's possible that you have PG in launchctl which may prevent you from stopping the server:

pg_ctl: server does not shut down

In that case let's remove PG from launchctl for now, you can add it back later by following the instructions given on brew info postgres:

launchctl unload -w ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist
rm ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist

Then try stopping the server again:

pg_ctl -D /usr/local/var/postgres stop -m fast

This would be good news:

pg_ctl: PID file "/usr/local/var/postgres/" does not exist
Is server running?

Assuming you're dealing with the same version numbers I'm dealing with (you probably aren't, so change them when running this on your machine), this is what the pg_upgrade command should look like when you run it:

$ pg_upgrade -b /usr/local/Cellar/postgresql/9.3.2/bin/ -B /usr/local/Cellar/postgresql/9.4.1/bin/ -d /usr/local/var/postgres.9.3.backup/ -D /usr/local/var/postgres

Lowercase flags (-b and -d) are for old binary and data directories respectively. Their uppercase counterparts are for their new equivalents.

You should see the following output immediately if the upgrade process is starting:

Performing Consistency Checks
Checking cluster versions                                   ok
Checking database user is a superuser                       ok
Checking for prepared transactions                          ok
Checking for reg* system OID user data types                ok
Checking for contrib/isn with bigint-passing mismatch       ok
Checking for invalid "line" user columns                    ok
Creating dump of global objects                             ok
Creating dump of database schemas
Checking for presence of required libraries                 ok
Checking database user is a superuser                       ok
Checking for prepared transactions                          ok

If pg_upgrade fails after this point, you must re-initdb the
new cluster before continuing.

Performing Upgrade
Analyzing all rows in the new cluster                       ok
Freezing all rows on the new cluster                        ok
Deleting files from new pg_clog                             ok
Copying old pg_clog to new server                           ok
Setting next transaction ID and epoch for new cluster       ok
Deleting files from new pg_multixact/offsets                ok
Copying old pg_multixact/offsets to new server              ok
Deleting files from new pg_multixact/members                ok
Copying old pg_multixact/members to new server              ok
Setting next multixact ID and offset for new cluster        ok
Resetting WAL archives                                      ok
Setting frozenxid and minmxid counters in new cluster       ok
Restoring global objects in the new cluster                 ok
Adding support functions to new cluster                     ok
Restoring database schemas in the new cluster
Creating newly-required TOAST tables                        ok
Removing support functions from new cluster                 ok
Copying user relation files
Setting next OID for new cluster                            ok
Sync data directory to disk                                 ok
Creating script to analyze new cluster                      ok
Creating script to delete old cluster                       ok

Upgrade Complete
Optimizer statistics are not transferred by pg_upgrade so,
once you start the new server, consider running:

Running this script will delete the old cluster's data files:

You're done!


You manually shut down PG during this upgrade so now it won't be running unless you follow the brew info postgres instructions:

ln -sfv /usr/local/opt/postgresql/*.plist ~/Library/LaunchAgents
launchctl load -w ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist

Once PG is running you could run the optimization script recommended by pg_upgrade. It was created in whichever directory you ran pg_upgrade in, and you can run it with:

This script will generate minimal optimizer statistics rapidly
so your system is usable, and then gather statistics twice more
with increasing accuracy.  When it is done, your system will
have the default level of optimizer statistics.

If you have used ALTER TABLE to modify the statistics target for
any tables, you might want to remove them and restore them after
running this script because they will delay fast statistics generation.

If you would like default statistics as quickly as possible, cancel
this script and run:
    "/usr/local/Cellar/postgresql/9.4.1/bin/vacuumdb" --all --analyze-only


You may encounter the following error:

Consult the last few lines of "pg_upgrade_server.log" for
the probable cause of the failure.

There seems to be a postmaster servicing the new cluster.
Please shutdown that postmaster and try again.
Failure, exiting

This means you have at least one PG server running. So go back to the beginning of this section and make real sure you shut down all your servers.

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