If the same identity is added concurrently by two threads (or by the
pool utility) INSERT might fail even though the SELECT was unsuccessful
before.
We are currently not able to lock the identities table in a portable way
(something like SELECT ... FOR UPDATE on MySQL).
There could, of course, be race conditions when enumerating the attributes,
but those probably don't matter (e.g. missing an attribute that was
concurrently added).
Transactions are more intended to revert multiple changes if anything
fails in the process.
If the provider has access to the full pool list, it can enumerate
them twice, for example to search for existing leases first, and
only search for new leases in a second step.
Fixes lease enumeration in attr-sql using multiple pools.
Add the possibility to group attributes by a name and assign these
groups to connections. This allows a more granular configuration of
which client will receive what atrributes.
Tobias Brunner