I looked into the odd behavior noted recently on pgsql-novice that the error context stack reported by plpgsql could differ between first and subsequent occurrences of the same error: http://www.postgresql.org/message-id/26370.1358539...@sss.pgh.pa.us
This seems to be specific to errors that are detected at plan time for a potentially-simple expression. The example uses "1/0" which throws an error when eval_const_expressions tries to simplify it. From plpgsql's viewpoint, the error happens when it tries to use GetCachedPlan() to get a plan tree that it can check for simple-ness. In this situation, we have not pushed _SPI_error_callback onto the error context stack, so the line it might contribute to the context report doesn't show up. However, exec_simple_check_plan is set up to mark the PLpgSQL_expr as non-simple at the outset, so that when it loses control due to the error, that's how the already-cached PLpgSQL_expr is marked. Thus, on a subsequent execution, we don't go through there but just pass off control to SPI_execute_plan --- and it *does* set up _SPI_error_callback before calling GetCachedPlan(). So now you get the additional line of context. There doesn't seem to be a comparable failure mode before 9.2, because in previous releases planning would always occur before we created a CachedPlanSource at all; so the failure would leave plpgsql still without a cached PLpgSQL_expr, and the behavior would be consistent across tries. My first thought about fixing this was to export _SPI_error_callback so that plpgsql could push it onto the context stack before doing GetCachedPlan. But that's just another piercing of the veil of modularity. What seems like a better solution is to export a SPI wrapper of GetCachedPlan() that pushes the callback locally. With a bit more work (a wrapper to get the CachedPlanSource list) we could also stop letting pl_exec.c #include spi_priv.h, which is surely a modularity disaster from the outset. Does anyone see a problem with back-patching such a fix into 9.2, so as to get rid of the context stack instability there? BTW, I'm also wondering if it's really necessary for plpython/plpy_spi.c to be looking into spi_priv.h ... regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers