2018-04-03 Meeting notes

Date

Apr 3, 2018

7am PST / 4pm CET

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Attendees

• @Josh Zamor (Deactivated)

• @Chongsun Ahn (Unlicensed)

• @Łukasz Lewczyński (Deactivated)

• @Craig Appl (Unlicensed)

• @Elias Muluneh

• @Paweł Albecki (Deactivated)

• @Sam Im (Deactivated)

• @Sebastian Brudziński

Goals

• See discussion items

Discussion items

Notes

Database migration speed

While testing latest code against production data for release testing, we found that fulfillment service wasn't starting in a short amount of time - the service was starting, but stuck in a long migration script.

This was because updates to schema / copying data was on a table which had 7+ million rows.  Through a bit of digging uncovered this recommendation:  https://dba.stackexchange.com/questions/52517/best-way-to-populate-a-new-column-in-a-large-table/52531#52531 . Which recommends duplicating the table, making the changes to the duplicate, and then replacing the old table with the new.

Question:  How do we ensure that when we're writing migrations, we're avoiding writing migrations that take hours?

We do know with our implementations that some hours of downtime are:

1. Monitor the flyway migration time (we'd need a threshold value and/or we'd need those 7 million rows to test against as an example).

2. Some teams won't allow certain statements to be used.

Prefer a mix of 1 and 2.

Where do we get the data for item #1?  For things like PoD line items that has a lot of data, we should commit to making performance data.

Action Items:

• How do we get the data for testing (when to decide to invest in creating performance data)?

• What are the exemplars for performant migrations / which types of migrations take a long time (is there a postgres DBA in the house?)

• Do we intend to move performance data into demo data - do we want to do that?  It's separate data sets, we think might like to combine for maintenance and consistency)

Migration testing

Current approach is to use a jenkins job that:

• starts the previous version of ref distro

• stops it

• starts the latest code which runs the new migrations

• failure is if a migration error is encountered, success otherwise

We also have experimented with a pattern of writing integration tests for individual migrations.

Some concerns with it:

• Migration's don't change, QA could find migration issues

• Are integration tests written for the edge cases

• We'd need more work:  write a test for each migration

Some concerns with the current approach:

• If there's no demo data, the tests don't cover much

• If a service isn't normally included in Ref Distro, it won't get covered.

• There have been some issues that have given us concern, and while we think we know what they are, we'd still like to revisit the approach.

Josh asks:  Central to any migration testing approach is having and loading data.  In the past I've used DbUnit to setup the database before test, and revert it to pre-test condition after the test has run.  Is this tool (or one like it) still valuable?

Action Items