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https://issues.apache.org/jira/browse/CASSANDRA-14406?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16602945#comment-16602945
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Benedict commented on CASSANDRA-14406:
--------------------------------------
Fixes:
# StorageProxy.mutate would have attempted a standardWritePerformer
maybeTryAdditionalReplicas for counters
# assureSufficientLiveReplicas and blockFor were not transient replication (or
pending replicas) aware
#* in the case of transient replication, this would mean we did not send enough
initial writes, because we capped ourselves to blockFor recipients
# AbstractWriteResponseHandler
#* was sending to all remaining replicas in case of failure to meet
consistency, not only those relevant for consistency
#* hasTransientResponse was racy - could have a transient response arrive after
checking condition
#** Have introduced {{Accumulator.snapshot}} to make working with it safely
more obvious
#** We take a snapshot, and look inside the list to decide if we have a
transient response
# sendMessagesToNonLocalDC was asserting no transient replicas - simply removed
the assertions, as logic is consistent
# Hints were not implemented, but mostly involved filtering them out; batch log
will be less trivial when implemented, as currently must hint
# Introduced separate threshold for cheap quorum upgrades
# There was a rare possible race condition when removing transient replication
from a keyspace, during which period we would not handle transient replicas
correctly
Nits:
# StorageProxy.mutate used a HashMap, when a List would suffice
Follow-ups pre-4.0:
# We should rename speculative_write_threshold (I thought we agreed on
transient_write_threshold)?
Follow-ups:
# EACH_QUORUM not implemented for transient replication; must either error or
implement before release
# we don’t limit our cheap quorum upgrade to the minimum number of additional
transient replicas, so a single missing response will result in all DCs
receiving an extra full write mutation, doubling cross-dc traffic for that write
# maybeTryAdditionalReplicas / sendMessagesToNonLocalDC are not DC aware in
their interactions, so transient writes incur more cross-DC traffic (ideally,
the proxies would be able to coordinate upgrading to a transient write)
# we don’t expose metrics around success/failure of cheap quorum
# transient write count isn’t incremented when we perform a non-additional
write (i.e. due to down full node)
> Transient Replication: Implement cheap quorum write optimizations
> -----------------------------------------------------------------
>
> Key: CASSANDRA-14406
> URL: https://issues.apache.org/jira/browse/CASSANDRA-14406
> Project: Cassandra
> Issue Type: Sub-task
> Components: Coordination
> Reporter: Ariel Weisberg
> Assignee: Blake Eggleston
> Priority: Major
> Fix For: 4.0
>
>
> Writes should never be sent to transient replicas unless necessary to satisfy
> the requested consistency level. Such as RF not being sufficient for strong
> consistency or not enough full replicas marked as alive.
> If a write doesn't receive sufficient responses in time additional replicas
> should be sent the write similar to Rapid Read Protection.
> Hints should never be written for a transient replica.
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