fix: address deadlock with concurrent snapshot creation #1908
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This commit addresses 2 issues: First, the deadlock occurred when trying to add where clauses to existing tables - we executed `ALTER TABLE` that took out an exclusive access lock over one table definition, then executed `SET TABLES` on a publication that requested shared access lock over all tables mentioned in the publication which includes tables that are already exclusively locked by another concurrent shape creation. This caused a deadlock. This was addressed by switching the order of alter table and alter publication. Second, there was a race condition when 2 new shapes tried updating the publication where clause and because it's done in a read-then-update way, not as a single statement, the read might have missed the concurrent update and the resulting state was wrong. This was addressed by a lock.
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msfstef
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Oct 31, 2024
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This commit addresses 2 issues:
First, the deadlock occurred when trying to add where clauses to existing tables - we executed
ALTER TABLEthat took out an exclusive access lock over one table definition, then executedSET TABLESon a publication that requested shared access lock over all tables mentioned in the publication which includes tables that are already exclusively locked by another concurrent shape creation. This caused a deadlock. This was addressed by switching the order of alter table and alter publication.Second, there was a race condition when 2 new shapes tried updating the publication where clause and because it's done in a read-then-update way, not as a single statement, the read might have missed the concurrent update and the resulting state was wrong. This was addressed by a lock.