I need my program code to ensure that certain part of logic is being executed within a transaction.

What query would tell me the current transaction ID / other information that would allow me to determine if I am in a transaction from within the transaction?

-- How to check if I am in a transaction?
  • Can't you structure your code so that your transaction boundaries are obvious? – Colin 't Hart May 31 '18 at 14:32

A simple way is to compare now() to statement_timestamp().

  • now() gives the current date and time (start of current transaction).
  • statement_timestamp() gives the current date and time (start of current statement).


SELECT now() = statement_timestamp();

SELECT now() = statement_timestamp();

The other alternative is to execute two queries:

SELECT txid_current();
SELECT txid_current();

and compare the resulting xid. If it is the same, then you are in a transaction.

The downside to the latter approach is that every txid_current() increments xid value and will further advance you to a wraparound.

  • I am running on Google Cloud SQL Postgres and I am able to more or less consistently reproduce SELECT now() = statement_timestamp(); returning TRUE when not in a transaction. – Gajus May 31 '18 at 15:49
  • Looks like you are right. My test was flawed. I have removed the comment about microseconds. – Gajus May 31 '18 at 16:09

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