TPA rolling updates v23

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The tpaexec update-postgres command performs a minor-version update of Postgres and related packages without interrupting overall cluster operations. Individual instances will be stopped and restarted during the update, but queries will be routed in such a way as to allow applications to continue database operations.

The exact procedure is architecture-specific.

BDR-Always-ON

For BDR clusters, the update process goes through the cluster instances one by one and does the following:

  1. Tell haproxy the server is under maintenance.
  2. If the instance was the active server, request pgbouncer to reconnect and wait for active sessions to be closed.
  3. Stop Postgres, update packages, and restart Postgres.
  4. Finally, mark the server as "ready" again to receive requests through haproxy.

BDR logical standby or physical replica instances are updated without any haproxy or pgbouncer interaction. Non-Postgres instances in the cluster are left alone.

You can control the order in which the cluster's instances are updated by defining the update_hosts variable:

$ tpaexec update-postgres ~/clusters/speedy \
  -e update_hosts=quirk,keeper,quaver

This may be useful to minimise lead/shadow switchovers during the update by listing the active BDR primary instances last, so that the shadow servers are updated first.

If your environment requires additional actions, the postgres-pre-update and postgres-post-update hooks allow you to execute custom Ansible tasks before and after the package installation step.

M1

For M1 clusters, update-postgres will first update the streaming replicas one by one, then perform a switchover from the primary to one of the replicas, update the primary, and switchover back to it again.

Package version selection

By default, tpaexec update-postgres will update to the latest available versions of the installed packages if you did not explicitly specify any package versions (e.g., Postgres, BDR, or pglogical) when you created the cluster.

If you did select specific versions, for example by using any of the --xxx-package-version options (e.g., postgres, bdr, pglogical) to tpaexec configure, or by defining xxx_package_version variables in config.yml, the update will do nothing because the installed packages already satisfy the requested versions.

In this case, you must edit config.yml, remove the version settings, and re-run tpaexec provision. The update will then install the latest available packages. You can still update to a specific version by specifying versions on the command line as shown below:

$ tpaexec update-postgres ~/clusters/speedy -vv         \
  -e postgres_package_version="2:11.6r2ndq1.6.13*"      \
  -e pglogical_package_version="2:3.6.11*"              \
  -e bdr_package_version="2:3.6.11*"

Please note that version syntax here depends on your OS distribution and package manager. In particular, yum accepts *xyz* wildcards, while apt only understands xyz* (as in the example above).

Note: see limitations of using wildcards in package_version in tpaexec-configure.

It is your responsibility to ensure that the combination of Postgres, BDR, and pglogical package versions that you request are sensible. That is, they should work together, and there should be an upgrade path from what you have installed to the new versions.

For BDR clusters, it is a good idea to explicitly specify exact versions for all three components (Postgres, BDR, pglogical) rather than rely on the package manager's dependency resolution to select the correct dependencies.

We strongly recommend testing the update in a QA environment before running it in production.