Bruce Momjian <bruce@momjian.us> writes: > Did we make any decision on this?
Hmm, that one seems to have slipped past me. I agree it doesn't look good. But why isn't the PreventInTransactionBlock() check blocking the command from even starting?
I assume because pgbench never sends a BEGIN command so the create database sees itself in an implicit transaction and happily goes about its business, expecting the system to commit its work immediately after it says it is done. But that never happens, instead the next command comes along and crashes the implicit transaction it is now sharing with the create database command. Create database understands how to rollback if it is the one that causes the failure but isn't designed to operate in a situation where it has to rollback because of someone else. That isn't how implicit transactions are supposed to work, whether in the middle of a pipeline or otherwise. Or at least that is my, and apparently CREATE DATABASE's, understanding of implicit transactions: one top-level command only.
Slight tangent, but while I'm trying to get my own head around this I just want to point out that the first sentence of the following doesn't make sense given the above understanding of implicit transactions, and the paragraph as a whole is tough to comprehend.
If the pipeline used an implicit transaction, then operations that have already executed are rolled back and operations that were queued to follow the failed operation are skipped entirely. The same behavior holds if the pipeline starts and commits a single explicit transaction (i.e. the first statement is BEGIN and the last is COMMIT) except that the session remains in an aborted transaction state at the end of the pipeline. If a pipeline contains multiple explicit transactions, all transactions that committed prior to the error remain committed, the currently in-progress transaction is aborted, and all subsequent operations are skipped completely, including subsequent transactions. If a pipeline synchronization point occurs with an explicit transaction block in aborted state, the next pipeline will become aborted immediately unless the next command puts the transaction in normal mode with ROLLBACK.
