Flush batched entries timer

[kevin-harrison]

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• You ran the local CI checker with ./check.sh with no errors
• You reference which issue is being closed in the PR text (if applicable)
• You updated the OmniPaxos book (if applicable)

Issues

Fix #127. Omnipaxos::tick() now also flushes batched log entries every flush_batch_tick_timeout ticks. This stops entries from being stuck in the batch buffer when there are no incoming proposals.

Breaking Changes

• Adds new field flush_batch_tick_timeout to ServerConfig.

[haraldng]

Looks good to me. I just want to confirm with you that we don't need to check that we're in the accept phase to flush these entries? Because they get buffered up in memory only in the accept phase.

[kevin-harrison]

Looks good to me. I just want to confirm with you that we don't need to check that we're in the accept phase to flush these entries? Because they get buffered up in memory only in the accept phase.

Yes exactly the entries will get flushed on entering the Prepare phase and will only start batching up in the Accept phase. But to be safe its probably better to only flush in the accept phase to prevent future bugs. I'll make that change now.

[haraldng]

Thanks!