sijie commented on a change in pull request #1808: Allow to configure sticky
reads
URL: https://github.com/apache/bookkeeper/pull/1808#discussion_r232922098
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File path:
bookkeeper-server/src/main/java/org/apache/bookkeeper/client/PendingReadOp.java
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@@ -96,13 +96,38 @@
this.ensemble = ensemble;
this.eId = eId;
+ long entryIdToConsiderForWriteSet = eId;
+
+ if (clientCtx.getConf().enableStickyReads
+ && lh.getLedgerMetadata().getWriteQuorumSize() ==
lh.getLedgerMetadata().getEnsembleSize()) {
+ // When sticky reads are enabled we want to make sure to take
+ // advantage of read-ahead (or, anyway, from effciencies in
+ // reading sequential data from disk through the page cache).
+ // For this, all the entries that a given bookie prefetches,
+ // should read from that bookie.
+ // For example, with e=2, w=2, a=2 we would have
+ // B-1 B-2
+ // e-0 X X
+ // e-1 X X
+ // e-2 X X
+ //
+ // In this case we want all the requests to be issued to B-1
(by
+ // preference), so that cache hits will be maximized.
+ //
+ // We can only enable sticky reads if the ensemble==writeQuorum
+ // otherwise the same bookie will not have all the entries
+ // stored
+ entryIdToConsiderForWriteSet = 0;
Review comment:
the change is to pick a "sticky" bookie. the idea here is to pick a fixed
"write set" (a certain read order). the write set is a sequence of bookie
index not fixed bookie addresses, so there is nothing to worry about about
"ensemble changes".
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