![]() Update: As of V2.0, only approach #2 to value locking is being maintained.Ĭommitting ON CONFLICT IGNORE first is now considered to be the best way of committing the code incrementally. When "V1.X" is referred to, there are actually two cumulative patchsets of "V1.X" (one for each approach to Value locking). Note that approach #1 and #2 to Value locking are being maintained in parallel. These commit messages are thought to be a useful way of gaining an understanding of how the proposed ON CONFLICT UPDATE/IGNORE patch fits together. The code is structured to be cumulative, and has extensive commit message commentary, to make its integration into PostgreSQL as straightforward as possible. Important: Note that git format-patch has been used to generate cumulative patch set revisions. This is primarily important for ETL-type use cases. It would be nice to offer an INSERT IGNORE - the ability to not proceed with insertion in respect of certain slots/rows proposed for insertion when doing so implies a unique violation must be thrown.The current looping approach really needs to loop over single values, making UPSERT of significant numbers of rows very slow. Support for UPSERT of multiple values in one operation is desirable.Don't burn through XIDs with expensive subtransactions - the existing, subxact-looping approach to UPSERT implies that XIDs are consumed at an intractably high rate (intractable for at least some use cases, like the multi-master replication conflict resolution use case). Avoid duplicate key violations that the implementation must trap and handle.Advance usability over the status quo - don't introduce a feature with significant foot-guns, unnecessary subtle behaviors, or big performance surprisesĪs outlined below, SQL MERGE seemingly doesn't meet this standard (principally because it lacks "the essential property of UPSERT", which appears to be in tension with supporting a fully flexible join).Again, this goal is a special case of our first primary goal. Avoid "unprincipled deadlocks" - deadlocks that the user has no reasonable way of avoiding.This goal is a special case of our first primary goal. Avoid having to invent " READ COMMITTED serialization failures".Don't be inferior in any way to existing, subxact-looping approach to UPSERT. In general, guarantee insert-or-update "atomicity" for the simple cases - guarantee one or the other of those two outcomes ("the essential property of UPSERT").The absence of this feature from Postgres has been a long-standing complaint from Postgres users. Examples include MySQL's INSERT.ON DUPLICATE KEY UPDATE, or VoltDB's UPSERT statement. One of those two outcomes must be guaranteed, regardless of concurrent activity, which has been called "the essential property of UPSERT". "UPSERT" is a DBMS feature that allows a DML statement's author to atomically either insert a row, or on the basis of the row already existing, UPDATE that existing row instead, while safely giving little to no further thought to concurrency. 6.2.3 Theoretical lock starvation hazards. ![]() 6.2.2 Visibility issues and the proposed syntax (WHERE clause/predicate stuff).6.2.1 Why still lock row when UPDATE predicate isn't satisfied?.6.2 Miscellaneous odd properties of proposed ON CONFLICT patch.6 Challenges, issues (with ON CONFLICT patch). ![]()
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