Hello,
I've been looking at the source code to the transaction engine / DMU
and was wondering what the purpose of dn->dn_assigned_txg was
for?
Looking through the source, I've found the dmu_tx structure but I'm
afraid I don't understand it fully and need some extra comments/help
here.
The reason I ask is this line of code within dmu_tx_try_assign()
(from opensolaris source) :
757 if (dn->dn_assigned_txg == tx->tx_txg - 1) {
If this condition is true, then tx->tx_needassign_txh is set, which
has an impact later on if dmu_tx_wait() is called.
In simple terms, what are we trying to test for here?
Which brings me onto the next part - for the most part, I see that
dmu_tx_wait ends up calling txg_wait_open() to move the
transaction engine along, but when tx_needassign_txh is set
we end up taking the other condition.
Could someone tell me what this branch of dmu_tx_wait() is designed
to do?
Apologies if these are dumb questions.
Many thanks,
Jason
