WAL sync checkpointing support #1928
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penberg
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This patch adds support for checkpointing during WAL sync, which allows
us to sync multiple checkpoint generations from the server.
The protocol is as follows:
1. A client uses the pull endpoint to fetch frames.
2. When we reach the end of a generation, the server returns "I am a teapot"
(yes, really) with a JSON containing the maximum generation number on the
server.
3. If we need to pull more generations, we first checkpoint the WAL on the
client, and then continue pulling frames from the newer generation.
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levydsa
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| Ok(PullResult::Frame(frame)) => { | ||
| insert_handle.insert(&frame)?; | ||
| frame_no += 1; | ||
| sync_ctx.durable_frame_num = frame_no; | ||
| } |
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We only need to insert here, apparently. Can we instead of maintaining the invariants of WalInsertHandle with a RefCell and check at runtime, use inherited mutability at comptime do the job by creating and dropping the handle on each frame? I introduced WalInsertHandle in a previous PR to be able to do that, but I might have encoded the wrong semantics. What you think?
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I am not sure I understand what you mean. If you want, please submit a PR to do what you propose and happy to merge if it's cleaner.
As Levy pointed out, we need to make sure we don't call `wal_insert_end()` unless we're still in a WAL insertion sesion.
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This pull request adds WAL sync checkpointing support.