Refactor pagecache <-> Wal redo communication #60
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kelvich
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Apr 24, 2021
After the rocksdb patch (commit 6aa38d3), the CacheEntry struct was used only momentarily in the communication between the page_cache and the walredo modules. It was in fact not stored in any cache anymore. For clarity, refactor the communication. There is now a WalRedoManager struct, with `request_redo` function, that can be used to request WAL replay of a particular page. It sends a request to a queue like before, but the queue has been replaced with tokio::sync::mpsc. Previously, the resulting page image was stored directly in the CacheEntry, and the requestor was notified using a condition variable. Now, the requestor includes a 'oneshot' channel in the request, and the WAL redo manager sends the response there.
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After the rocksdb patch (commit 6aa38d3), the CacheEntry struct was
used only momentarily in the communication between the page_cache and
the walredo modules. It was in fact not stored in any cache anymore.
For clarity, refactor the communication.
There is now a WalRedoManager struct, with
request_redofunction,that can be used to request WAL replay of a particular page. It sends
a request to a queue like before, but the queue has been replaced with
tokio::sync::mpsc. Previously, the resulting page image was stored
directly in the CacheEntry, and the requestor was notified using a
condition variable. Now, the requestor includes a 'oneshot' channel in
the request, and the WAL redo manager sends the response there.