How to find out PIDs of transactions older than the current?

On 25/04/14 13:26, Torsten F�rtsch wrote:

I think I can find out the transaction ids of concurrent transactions
older than the current one by:

select * from txid_snapshot_xip(txid_current_snapshot())
union
select * from txid_snapshot_xmax(txid_current_snapshot());

Now, I want to map these transaction ids to backend process ids.
pg_stat_activity does not provide the transaction id. So, I turned to
pg_locks.

select l.pid
from (
select * from txid_snapshot_xip(txid_current_snapshot())
union
select * from txid_snapshot_xmax(txid_current_snapshot())) tx(id)
join pg_locks l
on ( l.locktype='transactionid'
and l.transactionid::TEXT::BIGINT=tx.id);

This works. But my transaction ids are still far less than 2^32.

I think I got it. pg_locks.transactionid is a 4-byte quantity. But
I can safely ignore the upper half of the BIGINT that comes out of
txid_snapshot_xip(). So, the query becomes:

select l.pid
from (
select * from txid_snapshot_xip(txid_current_snapshot())
union
select * from txid_snapshot_xmax(txid_current_snapshot())) tx(id)
join pg_locks l
on ( l.locktype='transactionid'
and l.transactionid::TEXT::BIGINT=tx.id & (1::BIGINT<<32)-1)

Torsten

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