This attempts to add a README.md to help create consistent migrations
that maximize our test coverage and do not include unnecessary
statements.
It also adds a feature to have an `-- OLD DATA --` section as well
as a `-- NEW DATA --` section so that we can fix mistakes made in
previous snapshots (like a row that was forgotten to be added when a
table was created) without editing them going forward.
Change-Id: I28a786f8ef163cae1de1bb08f61af1e1104b0a88
The goal of this change is to improve the storagenode_storage_tallies table by removing the unneeded id column that is not being used but only taking up space, and also to add an index on a different column that needs it. Removing and adding a column seems simple, but ended up being more complicated because of some cockroachdb limitations.
The cockroachdb limitation when trying to remove a column from a table and create a new primary key are:
1. only allows primary key creation at table creation time (docs: https://www.cockroachlabs.com/docs/stable/primary-key.html)
2. table drop or rename is performed async and cannot be done in a transaction (issue: https://github.com/cockroachdb/cockroach/issues/12123, https://github.com/cockroachdb/cockroach/issues/22868)
To address these differences between cockroachdb and Postgres, this PR performs different migrations for the two database. The Postgres migration is straight forward and what you would expect, but the cockroach migration has two main changes:
1. To change a primary key, use the recommended process from the cockroachdb docs to create a new table with the new primary key you want and then migrate the data.
2. In order to do 1, we needed to do the new table renaming in a separate transaction from the data migration.
Ref: SM-65
Change-Id: Idc9aee3ab57aa4d5570e3d2980afea853cd966bf
