pgBouncer - A lightweight connection pooler for PostgreSQL

Highly visible missing features

Significant amount of users feel the need for those.

Waiting for contributors...

Bad naming in data strctures: * PgSocket->auth_user [vs. PgDatabase->auth_user] * PgSocket->db [vs. PgPool->db]
server_reset_query vs. per-db pool_mode . Session and transaction pooling mode should not use same server_reset_query . For session-pooling it should be DISCARD ALL , for non-session pooling it should be empty, but maybe there are setups where it is useful.

Solutions:
1. Just disable server_reset_query for non session-mode pools.
2. New option that disables server_reset_query for non-session-mode pools.
3. Two new settings for tx modes, keep server_reset_query for sessions: server_reset_query_transaction , server_reset_query_statement .
4. Three new separate settings for different modes:
  - server_reset_query_session
  - server_reset_query_transaction
  - server_reset_query_statement

other per-user settings
Maintenance order vs. lifetime_kill_gap: http://lists.pgfoundry.org/pipermail/pgbouncer-general/2011-February/000679.html
per_loop_maint/per_loop_activate take too much time in case of moderate load and lots of pools. Perhaps active_pool_list would help, which contains only pools touched in current loop.
new states for clients: idle and in-query. That allows to apply client_idle_timeout and query_timeout without walking all clients on maintenance time.
check if SQL error codes are correct
removing user should work - kill connections
keep stats about error counts
cleanup of logging levels, to make log more useful
to test: - signal flood - no mem / no fds handling
fix high-freq maintenance timer - it's only needed when PAUSE/RESUME/shutdown is issued.
Get rid of SBUF_SMALL_PKT logic - it makes processing code complex. Needs a new sbuf_prepare_*() to notify sbuf about short data. [Plain 'false' from handler postpones processing to next event loop.]
units for config parameters.

Load-balancing / failover. Both are already solved via DNS. Adding load-balancing config in pgbouncer might be good idea. Adding failover decision-making is not...
User-based route. Simplest would be to move db info to pool and fill username into dns.
some preliminary notification that fd limit is full
Move all "look-at-full-packet" situations to SBUF_EV_PKT_CALLBACK
pool_mode = plproxy - use postgres in full-duplex mode for autocommit queries, multiplexing several queries into one connection. Should result in more efficient CPU usage of server.
SMP: spread sockets over per-cpu threads. Needs confirmation that single-threadedness can be problem. It can also be that only accept() + login handling of short connection is problem that could be solved by just having threads for login handling, which would be lot simpler or just deciding that it is not worth fixing.