increase minimum version of PostgreSQL for Evergreen 3.4

[Galen Charlton]

Evergreen currently requires a minimum of version 9.4 for PostgreSQL, but that version will lose support in February 2020. It's time to bump up the minimum.

As of 28 May 2019, general consensus is to increase the minimum required version to 9.6 for several reasons:

- at least one enhancement (bug 1789679) requires Pg 9.5 or later
- Pg 9.6 includes various important performance enhancements
- A number of Evergreen sites are using Pg 9.6 in production

[Galen Charlton (gmc)]

The consensus is also that Pg 10 support is not fully baked yet, but putting my RM hat on, I do urge solidifying that support for the 3.4 release.

[Ben Shum (bshum)]

Initial branch started here: user/bshum/lp1830749-pg96-minimum

https://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/bshum/lp1830749-pg96-minimum

In this branch, I opted to change all the PG installs to include from the PostgreSQL community repo for consistency across all supported distros. Bumps minimum to PG 9.6 across the board.

[Jason Stephenson (jstephenson)]

I have added my signoff here: user/dyrcona/lp1830749-pg96-minimum-signoff

https://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/dyrcona/lp1830749-pg96-minimum-signoff

I tested this branch on an Ubuntu Xenial VM where Postgres had previously been installed from the Ubuntu repositories. I checked out Ben's branch, rebased it on master, did an upgrade of OpenSRF and Evergreen, then rebuilt the 9.5 database. I then installed the Postgres server prerequisites via the Makefile.install and did an upgrade of Pg 9.5 to Pg 9.6. I then remove the Pg 9.5 packages, and reconfigured Pg 9.6 to use the default port. All went well. (I did not test a fresh install, but presumably that would work with even less effort.)

I think this change warrants a release note about needing to upgrade your postgresql cluster afterward, so I'm not pushing to master and adding the needsreleasenote tag.

[Jason Stephenson (jstephenson)]

Unassigning myself as I meant to do that when I last commented on the bug. I wasn't planning on writing the release note, myself.

[Ben Shum (bshum)]

Looking back, the last time we specified a major minimum version for PostgreSQL was 9.4 for Evergreen 3.0.0.

For that change, there was not a separate release note added until the release notes were fully compiled, and it was the leading upgrade note entry:

"The minimum version of PostgreSQL required to run Evergreen 3.0 is PostgreSQL 9.4." (See: https://evergreen-ils.org/documentation/release/RELEASE_NOTES_3_0_0.html#_upgrade_notes)

In keeping with that, we could ask the RM to include a statement like this in the next release when the notes are being compiled and make it simple like:

"The minimum version of PostgreSQL required to run Evergreen 3.4 is PostgreSQL 9.6."

Separate issue, I did notice this other bug 1715503 from the past which sets up a check for if the database is not at least PG 9.4 prior to running the DB create. We should probably update that check for PG 9.6 as well. Patch forthcoming.

[Ben Shum (bshum)]

working: user/bshum/lp1830749-pg96-minimum-v2

https://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/bshum/lp1830749-pg96-minimum-v2

[Galen Charlton (gmc)]

Pushed to master for inclusion in 3.4. Thanks, Ben and Jason!

I will make sure that the final release notes include an appropriate upgrade section.