Fix Locking for ResignLeadership #20837
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jsteemann
reviewed
Apr 12, 2024
jsteemann
reviewed
Apr 12, 2024
jsteemann
reviewed
Apr 12, 2024
jsteemann
reviewed
Apr 12, 2024
arangod/Cluster/Maintenance.cpp
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| // check is we have collected information about this prototype already | ||
| auto it = prototypeShards.find(prototype); | ||
| if (it == prototypeShards.end()) { | ||
| auto protoCol = collections.get(prototype); |
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nit: I had a hard time read protoCol because I was intuitively thinking of protocol (as in HTTP, HTTPS, etc.). I get that it means protoCollection here, but naming it protoCol is slightly ambiguous, so I suggest using protoCollection instead.
jsteemann
reviewed
Apr 12, 2024
jsteemann
reviewed
Apr 12, 2024
| auto col = vocbase->lookupCollection(s); | ||
| if (col == nullptr) { | ||
| std::stringstream error; | ||
| error << "Failed to lookup local collection " << collection |
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Probably we should include the shard name in the error message here as well, to have more detail should this error happen, e.g.
"Failed to lookup shard s of local collection collection"
jsteemann
reviewed
Apr 12, 2024
jsteemann
reviewed
Apr 12, 2024
…rship-in-correct-order
Co-authored-by: Jan <jsteemann@users.noreply.github.com>
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Scope & Purpose
While streaming transactions and aql queries carefully lock multiple shards in a deterministic order, the maintenance did not care about such a order and just locked shards when resigning in any order. In fact the maintenance has no idea about distributeShardsLike and handles each shard of the shard group individually. A move shard requests locking of all shards in a shard group. This can lead to deadlocks with aql queries, since the locks are acquired in different orders.