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Benedict commented on CASSANDRA-6880: ------------------------------------- If we're doing per-cell locking, the likelihood of collision across different ostensible uncontended updates increases. So, I wonder if it mightn't be sensible to have a global set of locks with a larger domain? e.g. 1024 * concurrent writers, but shared across all tables (or even all keyspaces). A shared but larger address space should reduce the likelihood of collision, whilst also bounding the amount of per-table memory we use (128 * concurrent writers could be very expensive in a batch CLE environment with a lot of tables). Probably worth capping the number of stripes as well for the same reason. > counters++ lock on cells, not partitions > ---------------------------------------- > > Key: CASSANDRA-6880 > URL: https://issues.apache.org/jira/browse/CASSANDRA-6880 > Project: Cassandra > Issue Type: Improvement > Reporter: Aleksey Yeschenko > Assignee: Aleksey Yeschenko > Fix For: 2.1 beta2 > > > I'm starting to think that we should switch to locking by cells, not by > partitions, when updating counters. > With the current 2.1 counters, if nothing changes, the new recommendation > would become "use smaller partitions, batch updates to the same partition", > and that goes against what we usually recommend: > 1. Prefer wide partitions to narrow partitions > 2. Don't batch counter updates (because you risk to exaggerate > undercounting/overcounting in case of a timeout) > Locking on cells would cause C* to have to grab more locks for batch counter > updates, but would give us generally more predictable performance > (independent of partition wideness), and won't force people to remodel their > data model if they have often concurrently-updated counters in the same few > wide partitions. > (It's a small change, code-wise) -- This message was sent by Atlassian JIRA (v6.2#6252)