Currently, you can't run SET TRANSACTION in PL/pgSQL. A normal SQL
command run inside PL/pgSQL acquires a snapshot, but SET
TRANSACTION does not work anymore if a snapshot is set. Here is a patch
to work around that by handling this command separately. I have coded
this here bypassing SPI entirely. But there is some overlap with the
no_snapshot option in the patch "PL/pgSQL nested CALL with
transactions", so maybe a better solution will arise. This will also
inform how to tackle this in other PLs.
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Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services