When the topology coordinator refreshes load_stats, it caches load_stats
for every node. In case the node becomes unresponsive, and fresh
load_stats can not be read from the node, the cached version of
load_stats will be used. This is to allow the load balancer to
have at least some information about the table sizes and disk capacities
of the host.
During load_stats refresh, we aggregate the table sizes from all the
nodes. This procedure calls db.find_column_family() for each table_id
found in load_stats. This function will throw if the table is not found.
This will cause load_stats refresh to fail.
It is also possible for a table to have been dropped between the time
load_stats has been prepared on the host, and the time it is processed
on the topology coordinator. This would also cause an exception in the
refresh procedure.
This patch fixes this problem by checking if the table still exists.
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