On each shard of each node we store the view update backlogs of
other nodes to, depending on their size, delay responses to incoming
writes, lowering the load on these nodes and helping them get their
backlog to normal if it were too high.
These backlogs are propagated between nodes in two ways: the first
one is adding them to replica write responses. The seconds one
is gossiping any changes to the node's backlog every 1s. The gossip
becomes useful when writes stop to some node for some time and we
stop getting the backlog using the first method, but we still want
to be able to select a proper delay for new writes coming to this
node. It will also be needed for the mv admission control.
Currently, the backlog is gossiped from shard 0, as expected.
However, we also receive the backlog only on shard 0 and only
update this shard's backlogs for the other node. Instead, we'd
want to have the backlogs updated on all shards, allowing us
to use proper delays also when requests are received on shards
different than 0.
This patch changes the backlog update code, so that the backlogs
on all shards are updated instead. This will only be performed
up to once per second for each other node, and is done with
a lower priority, so it won't severly impact other work.
Fixes: scylladb/scylladb#19232Closesscylladb/scylladb#19268
d31437b589