· Jan 3, 2018

Freeze Query Plans on Upgrade from 2015.2 to 2017.1.2 or 2017.2.1

Will an upgrade from 2015.2 to 2017.1.2 or higher freeze the query plans from 2015.2? Is there some minimum source version where this will work?

Discussion (3)1
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You must be starting on a version that supports Frozen Query Plans.  In order to freeze a plan the query compiler needs to save some internal information so it can regenerate the same code on recompile.

2016.2 is the first version to support frozen plans.

Any upgrade from a version of 2016.2 or higher will automatically freeze all query plans.  This means you should see the exact same SQL performance after upgrade.  No more surprises with a query running much slower on the new version.  Of course that mean no improvement either until you test the plan to see if it has changed.

The documentation is misleading about this.  It says:

When you upgrade Caché to a new version, existing Query Plans are automatically frozen.

And later:

The earliest upgrade that performs this operation is an upgrade to 2017.1.0.

What it needs to say is:

The earliest upgrade that performs this operation is an upgrade from 2016.2.0.

The docs do use 2016.2 as the "from" version in their example, but not in a way that communicates how this nice feature won't help with upgrades from pre-2016.2 versions.

@Brendan Bannon - please draw this to the attention the InterSystems documentation team.

Above I've deliberately linked explicitly to the 2017.2 doc rather than to "latest" because I hope that in due course the latter will get corrected.