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When using a pipeline, a transaction starts from the first command and is committed with a Sync message or when the pipeline ends. Functions like IsInTransactionBlock() or PreventInTransactionBlock() were already able to understand a pipeline as being in a transaction block, but it was not the case of CheckTransactionBlock(). This function is called for example to generate a WARNING for SET LOCAL, complaining that it is used outside of a transaction block. The current state of the code caused multiple problems, like: - SET LOCAL executed at any stage of a pipeline issued a WARNING, even if the command was at least second in line where the pipeline is in a transaction state. - LOCK TABLE failed when invoked at any step of a pipeline, even if it should be able to work within a transaction block. The pipeline protocol assumes that the first command of a pipeline is not part of a transaction block, and that any follow-up commands is considered as within a transaction block. This commit changes the backend so as an implicit transaction block is started each time the first Execute message of a pipeline has finished processing, with this implicit transaction block ended once a sync is processed. The checks based on XACT_FLAGS_PIPELINING in the routines checking if we are in a transaction block are not necessary: it is enough to rely on the existing ones. Some tests are added to pgbench, that can be backpatched down to v17 when \syncpipeline is involved and down to v14 where \startpipeline and \endpipeline are available. This is unfortunately limited regarding the error patterns that can be checked, but it provides coverage for various pipeline combinations to check if these succeed or fail. These tests are able to capture the case of SET LOCAL's WARNING. The author has proposed a different feature to improve the coverage by adding similar meta-commands to psql where error messages could be checked, something more useful for the cases where commands cannot be used in transaction blocks, like REINDEX CONCURRENTLY or VACUUM. This is considered as future work for v18~. Author: Anthonin Bonnefoy Reviewed-by: Jelte Fennema-Nio, Michael Paquier Discussion: https://postgr.es/m/CAO6_XqrWO8uNBQrSu5r6jh+vTGi5Oiyk4y8yXDORdE2jbzw8xw@mail.gmail.com Backpatch-through: 13 |
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