XLog: how to log?

Hackers,

I'm trying to figure out how to log the subtransaction operations.

A simple idea would be to add the committed subxact Xids to the
xl_xact_commit and xl_xact_abort structs.  However, this will be a
variable length array, and those structs already have variable length
arrays at the end (filenodes to drop).  I don't see how would I overlay
that into a C struct.

A different idea would be to write a XLog record for subxact aborts
(which would include Xids of all committed child subxacts), and
at main transaction commit write another (different) XLog record, where
XLogRecord.Xid = mainTransactionXid, which would carry the committed
subtransactions.

Does this make any sense?  Ideas, comments?

-- 
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"No reniegues de lo que alguna vez creíste"