This patch makes storage proxy to choose replicas to read from base on
their cache hit rates. Replicas with higher cache hit rates will see
more requests while replicas with lower hit rates will see less. Local
node has a special bonus and will get more requests even if another node
has slightly higher cache hit rate (same goes for local vs remote DC),
but after the patch it is no longer guarantied that a coordinator node
will be chosen as a replica for the read (if the feature is enabled).
Currently storage proxy has to loop over remaining replicas to search
for suitable extra replica, but doing it in filter_for_query() is
extremely easy, so do it there instead.
Merge filter_for_query_dc_local() functionality into filter_for_query().
This is more efficient since filter_for_query_dc_local() partitions
endpoints into 'local' and 'remote' set but filter_for_query() already
does it for CL=LOCAL so for such queries we needlessly do it twice.
filter_for_query() gets sorted by preference list of endpoints and
should preserve that order after filtering out non local endpoints for
local query. partition() does not guaranty this while stable_partition()
does, so use it instead.
Fixes#1450.
Message-Id: <20160713100909.GM10767@scylladb.com>
This is kind of sorting, so it belongs there, but it also fixes a bug in
storage_proxy::get_read_executor() that assumes filter_for_query() do
not change order of nodes in all_nodes when extra replica is chosen.
Otherwise if coordinator ip happens to be last in all_nodes then it will
be chosen as extra replica and will be quired twice.
Message-Id: <1460549369-29523-1-git-send-email-gleb@scylladb.com>
During bootstrapping additional copies of data has to be made to ensure
that CL level is met (see CASSANDRA-833 for details). Our code does
that, but it does not take into account that bootstraping node can be
dead which may cause request to proceed even though there is no
enough live nodes for it to be completed. In such a case request neither
completes nor timeouts, so it appear to be stuck from CQL layer POV. The
patch fixes this by taking into account pending nodes while checking
that there are enough sufficient live nodes for operation to proceed.
Fixes#965
Message-Id: <20160303165250.GG2253@scylladb.com>
