Re: 7.4 Press Release -- Draft #4
От | Robert Treat |
---|---|
Тема | Re: 7.4 Press Release -- Draft #4 |
Дата | |
Msg-id | 1059484111.22265.826.camel@camel обсуждение исходный текст |
Ответ на | Re: 7.4 Press Release -- Draft #4 (Gavin Sherry <swm@linuxworld.com.au>) |
Список | pgsql-advocacy |
On Mon, 2003-07-28 at 19:16, Gavin Sherry wrote: > On Mon, 28 Jul 2003, Josh Berkus wrote: > > > Robert, > > > > > Aside from spec compliance, whats the bonus for having it then? Or put a > > > better way, why/when would I want to use this? > > > > One scenario: You have 5 PostgreSQL servers connecting to one SAN or NAS > > which is your /data directory for a single database. You use your > > middleware to distribute requests among the servers; One server gets data > > write requests, the other 4 get read-only requests. > > > > However, you want to make sure that if your middleware hiccups you don't > > corrupt the database files. For this, setting 4 of the servers to "Read Only > > Transactions" would be useful. > > That will not work because the writer maintains a cache of data to write > and worse case scenario, the data only gets written to data files every > CHECKPOINT. This means that your four readers are returning corrupted > data. Moreover, the readers do not expect the data to change undernearth > them, as they maintain caches and would have no mechanism to invalidate > that cache upon external file system changes. Load balancing and > clustering is hard :P. > > It is, however, generally used with READ UNCOMMITTED transactions. In > fact, SQL99 necessitates READ ONLY for READ UNCOMMITTED isolation level > (READ UNCOMMITTED allows you to see uncommitted data modifications). > I was really looking for the nie one-line answer that might go in a press release, but I don't think this is one of those types of features. Sure, it can be useful in some places, and it adds to spec compliance, but I don't think it is big enough to need mentioning in the press release. Robert Treat -- Build A Brighter Lamp :: Linux Apache {middleware} PostgreSQL
В списке pgsql-advocacy по дате отправления: