Clash Royale CLAN TAG#URR8PPP

Do stored procedures run in database transaction in Postgres?

If a stored procedure fails in middle, are changes at that point from the beginning of SP rolled back implicitly or do we have to write any explicit code to make sure that SP runs in a database transaction only?

1 Answer
1

Strictly speaking Postgres does not currently (up to and including version 10) have "stored procedures" as defined in the ANSI standard. Everything is done with "functions" instead, which provide much of the same functionality (and more) as other RDBMS provide with stored procedures. The main difference being transaction handling.

True stored procedures are finally introduced with Postgres 11:

Functions are atomic in Postgres and automatically run inside their own transaction unless called within an outer transaction. They always run inside a single transaction and succeed or fail completely. Consequently, one cannot begin or commit transactions within the function. And commands like VACUUM or CREATE INDEX CONCURRENTLY which cannot run within a transaction block are not allowed.

VACUUM

CREATE INDEX CONCURRENTLY

Per documentation on PL/pgSQL:

Functions and trigger procedures are always executed within a
transaction established by an outer query — they cannot start or
commit that transaction, since there would be no context for them to
execute in. However, a block containing an EXCEPTION clause
effectively forms a subtransaction that can be rolled back without
affecting the outer transaction.

EXCEPTION

Error handling:

By default, any error occurring in a PL/pgSQL function aborts
execution of the function, and indeed of the surrounding transaction
as well. You can trap errors and recover from them by using a BEGIN
block with an EXCEPTION clause.

BEGIN

EXCEPTION

There are special exceptions, including but not limited to:

changes made to a sequence

Important: Some PostgreSQL data types and functions have special rules
regarding transactional behavior. In particular, changes made to a
sequence (and therefore the counter of a column declared using serial)
are immediately visible to all other transactions and are not rolled
back if the transaction that made the changes aborts.

serial

prepared statements

dblink calls (or similar)

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