DbLedgerStorage -- ReadCache#843
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sijie
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Dec 13, 2017
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LGTM +1
one question: I think this ReadCache is general can be shared with different ledger storage implementations, right?
| private final List<ConcurrentLongLongPairHashMap> cacheIndexes; | ||
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| private int currentSegmentIdx; | ||
| private AtomicInteger currentSegmentOffset = new AtomicInteger(0); |
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yes, I thought it was being reassigned but it's not.
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Yes, same for |
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@merlimat we can consider sharing the components with other implementations once the db ledger storage change is merged. |
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merging this now to unblock subsequent db ledger storage changes. |
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Adds a
ReadCacheclass to be used from LedgerStorage.The read cache is used when doing read-ahead caching after reading one entry.
The idea is that entries for the same ledger as stored in order (for each flush cycle, eg: 1min). When reading 1 entry, we expect the client to read all subsequent entries. We can then skip the RocksDb
get()to fetch the index of the entries, by just keep reading from the entryLog, and exploiting page cache and seqeuential reads. The entries are then added to this ReadCache, where they will looked when the request for next entry comes in.This implementation is based on dividing the memory into multiple segments. Whenever the read cache is full, the oldest segment gets recycled and overwritten with new entries.