Pgpool-II 3.2 is the latest stable version released in Aug 2012.
On Memory Query Cache
- New fast query cache !
- On memory query cache is faster because cache storage is on memory. Moreover you don't need to restart pgpool-II when the cache is outdated because the underlying table gets updated.
- On memory cache saves pair of SELECT statements (with its Bind parameters if the SELECT is an extended query). If the same SELECTs comes in, it returns the value from cache. Since no SQL parsing nor access to PostgreSQL are involed, it's extremely fast.
- Choosing cache storage
- You can choose a cache storage: shared memory or memcached (you can't use the both).
- Query cache with shared memory is fast and easy because you don't have to install and config memcached, but restricted the max size of cache by the one of shared memory. Query cache with memcached needs a overhead to access network, but you can set the size as you like.
"Watchdog" is a sub process of pgpool-II aiming for adding high availability feature to it. Features added by watchdog include:
- Life checking of pgpool service
- Watchdog monitors responses of pgpool service rather than process. It sends queries to PostgreSQL via pgpool which is being monitored by watchdog and watchdog checks the response.
- Also watchdog monitors connections to up stream servers (application servers etc.) from the pgpool.
- The connection between the up stream servers and the pgpool is monitored as service of pgpool.
- Mutually monitoring of watchdog processes
- Watchdog processes exchange information on the monitored servers to keep the information up to date, and to allow watchdog processes to mutually monitor each other.
- Changing active/standby state in case of certain faults detected
- When a fault is detected in the pgpool service, watchdog notifies the other watchdogs of it. Watchdogs decide the new active pgpool if previous active pgpool is broken by voting and change active/standby state.
- Automatic virtual IP address assigning synchronous to server switching
- When a standby pgpool server promotes to active, the new active server brings up virtual IP interface. Meanwhile, the previous active server brings down the virtual IP interface.
- This enables the active pgpool to work using the same IP address even when servers is switched over.
- Automatic registration of a server as standby in recovery
- When broken server recovers or new server is attached, the watchdog process notifies the other watchdog process along with information of the new server, and the watchdog process receives information on the active server and other servers. Then, the attached server is registered as standby.