Re: Review Request 58036: Ensure enum tables are complete after a snapshot restore.

[Zameer Manji <zm...@apache.org>]

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This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/58036/
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(Updated March 30, 2017, 10:36 a.m.)


Review request for Aurora, Santhosh Kumar Shanmugham and Stephan Erb.


Summary (updated)
-----------------

Ensure enum tables are complete after a snapshot restore.


Bugs: AURORA-1912
    https://issues.apache.org/jira/browse/AURORA-1912


Repository: aurora


Description (updated)
-------

In our in memory database, we model enums as two column tables. The two columns
would be `id` which corresponds to the integer value in the thrift enum and
`name` which is the all caps string name of the enum. For example to model the
`JobUpdateStatus` enum we have a table called `job_update_statuses`. In there
the `ROLLING_FORWARD` enum is modeled as a row `(0, "ROLLING_FORWARD")`. Other
tables reference the enum table via the id.

When we prepare storage on startup the `DbStorage` starts up. It does two
things:
1. Load in the schema.
2. Populate the enum tables.

This ensures that when we insert values into the database, the enum refernces
will be valid.

However, before we restore from a Snapshot with the `dbScript` field, we blow all
of that data away and restore what was in the snapshot:
````
try (Connection c = ((DataSource) store.getUnsafeStoreAccess()).getConnection()) {
  LOG.info("Dropping all tables");
  try (PreparedStatement drop = c.prepareStatement("DROP ALL OBJECTS"))
    drop.executeUpdate();
  }
````

This means that if we add a new enum value, and then restore from a snapshot,
that enum value will not exist in the table any more. We could address this by
saying that every enum value addition requires a migration. However instead I
propose not blowing away the work done by `DbStorage` instead and re-hydrating
the enum tables.

To do this I extracted the logic into a new class `EnumBackfill`. Restoring from
a snapshot calls this after the migrations are done. The underlying SQL was
changed from `INSERT` to `MERGE` to make this work.


Diffs
-----

  src/main/java/org/apache/aurora/scheduler/storage/backup/TemporaryStorage.java 36a1bd5c784ed0febebccfd22e5064f0b2e3106f 
  src/main/java/org/apache/aurora/scheduler/storage/db/DbModule.java d1a196419b67108ee2bb778f83a2993e2e5ee83b 
  src/main/java/org/apache/aurora/scheduler/storage/db/DbStorage.java 923e904f396724b9dde4a330ef312a6aae2c02a6 
  src/main/java/org/apache/aurora/scheduler/storage/db/EnumBackfill.java PRE-CREATION 
  src/main/java/org/apache/aurora/scheduler/storage/log/SnapshotStoreImpl.java 81a8cca6974e33c774473a4990e0e981cf6ddee6 
  src/main/resources/org/apache/aurora/scheduler/storage/db/EnumValueMapper.xml 153fd26c27275c46b190e71d8a5736153f2c2d18 
  src/test/java/org/apache/aurora/scheduler/storage/backup/RecoveryTest.java 42615da54096d5b06c7989cb30fc3cfbe59bc1b9 
  src/test/java/org/apache/aurora/scheduler/storage/db/DbStorageTest.java f26529c76214c8f22563f04a197798c82d341b49 
  src/test/java/org/apache/aurora/scheduler/storage/log/SnapshotStoreImplIT.java ca9525665805a33b4a322a72022ff037f0dd2a94 


Diff: https://reviews.apache.org/r/58036/diff/2/


Testing
-------

existing tests and e2e tests

I also added a new enum value to `JobUpdateStatus` and observed it was correctly loaded in.


Thanks,

Zameer Manji