This post was originally published as a Gist which I since forgot about and accidentally rediscovered recently when the need arose to resolve a similar accidental upgrade. I felt like it deserved to live somewhere where there is a chance I might update it.
In Homebrew 1.5 and above, there’s a new process to upgrade your
Postgres database across major versions using the
command which was recently added by Mike McQuaid.
This is a fantastic one-step improvement over the lengthy guide you’ll see below, but since this new command isn’t foolproof (it will fail if you haven’t killed all processes connected to your database) it seems like a good idea to still understand the way it works behind the scenes.
I’ve learned a cool new trick from Homebrew’s upgrade command however and you can find it in the last section of this updated post.
Accidental Homebrew Upgrades
This guide assumes that you recently ran
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.
Some of the common signs of this issue are the following statements in your logs:
1 2 FATAL: database files are incompatible with server DETAIL: The data directory was initialized by PostgreSQL version 9.5, which is not compatible with this version 9.6.
1 2 PG::InternalError: ERROR: incompatible library "/usr/local/lib/postgresql/dict_snowball.so": version mismatch DETAIL: Server is version 9.5, library is version 9.6.
No need to panic. Your data should be fine. While you’ve upgraded the Postgres library, your existing databases have not been removed. They simply need to be upgraded to run with the new library.
Important Caveat for Non-Incremental Upgrades
The process I describe below will work for incremental version updates: for example 9.5 to 9.6. But it will probably not work if you jump versions: for example 9.5 to 10.0.
In order to upgrade properly you will first need to downgrade the Postgres version in Homebrew to the version directly after the one of your data directory.
How do you figure out what version your data directory uses? Ask it.
1 2 cat /usr/local/var/postgres/PG_VERSION 9.5
There we go. And what is your currently activated Postgres version in Homebrew?
1 2 $ psql --version psql (PostgreSQL) 9.6.6
Good. If you find yourself one step further than you should be, say
10.0 like I was. You can do the following to step back down to
1 2 3 4 brew uninstall postgresql brew install email@example.com brew services start firstname.lastname@example.org brew link email@example.com --force
Couldn’t you use this to go back to Postgres 9.5? Yes, you could. But it’s never a bad idea to stay up to date with newer versions, so why not use the opportunity to be less worried about upgrades?
Now, check the active version of Postgres with:
1 2 $ psql --version psql (PostgreSQL) 9.6.6
You can check all the versions of postgres that are installed in Homebrew with:
1 2 3 $ brew list --versions | grep postgres postgresql 9.4.5_2 9.5.0 9.5.4_1 9.5.3 firstname.lastname@example.org 9.6.6
In this case you can see that I don’t have Postgres 9.6 installed in the
usual postgres formula, since I had to specifically install that version
in order to be able to upgrade from 9.5 with
brew install email@example.com.
So there are 5 different versions of PostgreSQL installed on my machine in different subfolders. We can find out where those are with:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 $ brew info postgresql postgresql: stable 10.1 (bottled), HEAD Object-relational database system https://www.postgresql.org/ Conflicts with: postgres-xc (because postgresql and postgres-xc install the same binaries.) /usr/local/Cellar/postgresql/9.4.5_2 (3,030 files, 33.6MB) Poured from bottle on 2015-11-09 at 05:23:00 /usr/local/Cellar/postgresql/9.5.0 (3,122 files, 34.9MB) Poured from bottle on 2016-02-11 at 22:16:06 /usr/local/Cellar/postgresql/9.5.3 (3,142 files, 35.0MB) Poured from bottle on 2016-06-16 at 16:19:04 /usr/local/Cellar/postgresql/9.5.4_1 (3,147 files, 35MB) Poured from bottle on 2016-10-08 at 02:50:55 ...
As you can see I have my old versions installed in
/usr/local/Cellar/postgresql/. And what about this new
That one’s in a standalone directory:
1 2 3 4 5 6 7 $ brew info firstname.lastname@example.org email@example.com: stable 9.6.6 (bottled) [keg-only] Object-relational database system https://www.postgresql.org/ /usr/local/Cellarfirstname.lastname@example.org/9.6.6 (3,273 files, 36.8MB) * Poured from bottle on 2018-02-07 at 09:24:03 ...
One final check to make sure we have the correct versions of the Postgres commands running:
1 2 psql --version psql (PostgreSQL) 9.6.6
This means that the
pg_upgrade binary we’ll be using is also the new
one. But let’s not assume:
1 2 pg_upgrade --version pg_upgrade (PostgreSQL) 9.6.6
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
initdb) it could squash all your existing data.
First I recommend moving your existing data to a directory with a different name:
1 mv /usr/local/var/postgres/ /usr/local/var/postgres.9.5.backup/
Now that the old data directory has been “moved”, you can safely create a brand new clean database:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 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 or 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
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
password field in
database.yml or leave it *completely empty.
Shutting Things Down
First we have to make sure both database servers are not running when we do the upgrade:
1 2 pg_ctl -D /usr/local/var/postgres stop -m fast pg_ctl -D /usr/local/var/postgres.9.5.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:
1 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:
1 2 launchctl unload -w ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist rm ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist
Then try stopping the server again:
1 pg_ctl -D /usr/local/var/postgres stop -m fast
This would be good news:
1 2 pg_ctl: PID file "/usr/local/var/postgres/postmaster.pid" does not exist Is server running?
If you’re using a recent version of Homebrew (as you should), then it’s likely you’re using Homebrew Services instead of launchctl to manage persistent processes like postgres. So use this instead:
1 brew services stop postgresql
While Homebrew Services should do the job of stopping postgres, it’s not
guaranteed that you don’t have a server process connected to postgres
and locking it’s
pid (process ID) file. It’s always a good idea to
check for that file which may exist at
/usr/local/var/postgres/postmaster.pid. If it does, remove it with
rm /usr/local/var/postgres/postmaster.pid and you’ll save yourself
some surprises later on.
I’ve based this article on the fairly detailed pg_upgrade guide in the PostgreSQL documentation. If you have specific needs (very large data directory for example), you should consult it too. This section is also not specific to a macOS Homebrew install of Postgres since it uses the same commands you should be able to use on other operating systems like Linux.
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:
1 2 3 4 $ pg_upgrade -b /usr/local/Cellar/postgresql/9.5.4_1/bin/ \ -B /usr/local/Cellaremail@example.com/9.6.6/bin/ \ -d /usr/local/var/postgres.9.5.backup/ \ -D /usr/local/var/postgres
Lowercase flags (
-d) are for old
directories respectively. Their uppercase counterparts are for their new
I really dislike short form flags because they make self-descriptive discovery very difficult so here is the alternative with long-form flags:
1 2 3 4 $ pg_upgrade --old-bindir /usr/local/Cellar/postgresql/9.5.4_1/bin/ \ --new-bindir /usr/local/Cellarfirstname.lastname@example.org/9.6.6/bin/ \ --old-datadir /usr/local/var/postgres.9.5.backup/ \ --new-datadir /usr/local/var/postgres \
How nice is this?
You should see the following output immediately if the upgrade process is starting:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 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 ok 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 ok Creating newly-required TOAST tables ok Removing support functions from new cluster ok Copying user relation files ok 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: analyze_new_cluster.sh Running this script will delete the old cluster's data files: delete_old_cluster.sh
You manually shut down PG during this upgrade so now it won’t be running
unless you follow the (old)
brew info postgres instructions:
1 2 ln -sfv /usr/local/opt/postgresql/*.plist ~/Library/LaunchAgents launchctl load -w ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist
With Homebrew Services, the operation is even simpler:
1 2 brew services start postgresql ==> Successfully started `postgresql` (label: homebrew.mxcl.postgresql)
Once PG is running you could run the optimization script recommended by
pg_upgrade. It was created in whichever directory you ran
in, and you can run it with:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ./analyze_new_cluster.sh 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/9.5.4_1/bin/vacuumdb" --all --analyze-only (...)
You may encounter the following error:
1 2 3 4 5 6 7 *failure* 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.
You can also check this
pg_upgrade_server.log file to be certain of
the issue. It should be located in
/usr/local/var/log/pg_upgrade_server.log but you can always use the
find command to locate it:
1 find / -name pg_upgrade_server.log
brew postgresql-upgrade-database, this log should contain
the reason the upgrade process failed as well as the actual command
used, which will be very useful for you to restart the upgrade process
I’ve found that running
brew postgresql-upgrade-database again after
an initial failed attempt usually results in an error message saying
that the data was already upgraded when it’s not actually true or at
least the process hasn’t fully completed.
You can see how this script works by checking its source code. It
seems like it’s comparing the Homebrew-installed version to the
version of the currently active Postgres database inside of the
data directory. It references the PostgreSQL documentation upgrade article
as well. The only notable difference with the instructions I’ve listed above
is the use of the
-j flag, which defines how many threads or processes the
pg_upgrade command will use. Homebrew sets that number to
Hardware::CPU.cores.to_s which would be 2, 4, 6 or more CPU cores your machine
may have to handle CPU-intensive tasks like these.
However I’d recommend not doing this since you may have operations already using some CPU on your machine. My best tip is to use one less core than your total, which I learned from this excellent Thoughbot blog post on parallel RubyGem install configuration for Bundler:
1 2 3 number_of_cores=`sysctl -n hw.ncpu` echo "$(expr $number_of_cores - 1)" 11
So here’s the final command in its full glory for all of you who skipped straight to the bottom of this post:
1 2 3 4 5 $ pg_upgrade --old-bindir /usr/local/Cellar/postgresql/9.5.4_1/bin/ \ --new-bindir /usr/local/Cellaremail@example.com/9.6.6/bin/ \ --old-datadir /usr/local/var/postgres.9.5.backup/ \ --new-datadir /usr/local/var/postgres \ --jobs $(expr $(sysctl -n hw.ncpu) - 1)