When a node reshards (i.e., restarts with a different number of CPUs), and
is in the middle of building a view for a pre-existing table, the view
building needs to find the right token from which to start building on all
shards. We ran the same code on all shards, hoping they would all make
the same decision on which token to continue. But in some cases, one
shard might make the decision, start building, and make progress -
all before a second shard goes to make the decision, which will now
be different.
This resulted, in some rare cases, in the new materialized view missing
a few rows when the build was interrupted with a resharding.
The fix is to add the missing synchronization: All shards should make
the same decision on whether and how to reshard - and only then should
start building the view.
Fixes#3890Fixes#3452
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20181028140549.21200-1-nyh@scylladb.com>
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