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ConversationStore.Cassandra: Explain en masse locks acquisition #5235

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ConversationStore.Cassandra: Explain en masse locks acquisition #5235

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16 changes: 16 additions & 0 deletions libs/wire-subsystems/src/Wire/ConversationStore/Cassandra.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -1112,6 +1112,14 @@ interpretConversationStoreToCassandraAndPostgres client = interpret $ \case
True -> interpretConversationStoreToPostgres $ ConvStore.getConversationEpoch cid
GetConversations cids -> do
logEffect "ConversationStore.GetConversations"
-- Here we must take all these locks because its not sufficient to just
-- lookup in both DBs and then de-dupe to deal with this edge case:
--
-- 1. During migration, the delete in Cassandra gets lost
-- 2. Before the next lookup, the conversation gets deleted from PG and the
-- delete in Cassandra still gets lost
-- 3. If we don't lock and cleanup, we are at a risk of resurrecting this
-- conv.
withMigrationLocksAndConvCleanup client LockShared (Seconds 2) cids $ do
let indexByConvId = foldr (\storedConv -> Map.insert storedConv.id_ storedConv) Map.empty
cassConvs <- indexByConvId <$> localConversations client cids
Expand Down Expand Up @@ -1181,6 +1189,14 @@ interpretConversationStoreToCassandraAndPostgres client = interpret $ \case
True -> interpretConversationStoreToPostgres (ConvStore.isConversationAlive cid)
SelectConversations uid cids -> do
logEffect "ConversationStore.SelectConversations"
-- Here we must take all these locks because its not sufficient to just
-- lookup in both DBs and then de-dupe to deal with this edge case:
--
-- 1. During migration, the delete in Cassandra gets lost
-- 2. Before the next lookup, the conversation gets deleted from PG and the
-- delete in Cassandra still gets lost
-- 3. If we don't lock and cleanup, we are at a risk of resurrecting this
-- conv.
withMigrationLocksAndConvCleanup client LockShared (Seconds 2) cids $ do
cassConvs <- embedClient client $ localConversationIdsOf uid cids
pgConvs <- interpretConversationStoreToPostgres $ ConvStore.selectConversations uid cids
Expand Down