Significant state about forks is stored in ephemeral blockHistory

[flux627]

Rollbacks can only be initiated when the action reader sees them happening, with its occurrence stored in AbstractActionReader#blockHistory. If the indexState is on a forked block at startup, then the action reader will not have any way of knowing this and send a block whose blockHash does not match, and it is not trivial to determine how far the Handler needs to roll back.

[jeffreyssmith2nd]

It's been awhile since we discussed it, but we talked at one point about persisting blockHistory to Postgres. Would that be one potential solution here?

[flux627]

blockHistory is something that's in the ActionReader. Maybe we could make a abstract subclass of the AbstractActionReader called the AbstractPostgresActionReader or something, that connects to a postgres database for persisting its own state, but I think a cleaner solution would be to:

• Persist lastIrreversibleBlock data to indexState
• Detect this case when the ActionHandler processes its first block, and rolls back to the lastIrreversibleBlock number from indexState
• Request the next block needed after the ActionHandler's rollback

[jeffreyssmith2nd]

Step 1 will be done in #132