On Wed, Oct 14, 2015 at 12:41 PM, Victor Wagner <vi...@wagner.pp.ru> wrote:
> On 2015.08.18 at 07:18:50 +0300, Victor Wagner wrote: > > > Rationale > > ========= > > > > Since introduction of the WAL-based replication into the PostgreSQL, it > is > > possible to create high-availability and load-balancing clusters. > > > > However, there is no support for failover in the client libraries. So, > only > > way to provide transparent for client application failover is IP address > > migration. This approach has some limitation, i.e. it requires that > > master and backup servers reside in the same subnet or may not be > > feasible for other reasons. > > > > Commercial RDBMS, such as Oracle, employ more flexible approach. They > > allow to specify multiple servers in the connect string, so if primary > > server is not available, client library tries to connect to other ones. > > > > This approach allows to use geographically distributed failover clusters > > and also is a cheap way to implement load-balancing (which is not > > possible with IP address migration). > > > > Attached patch which implements client library failover and > loadbalancing as was described in the proposal > <20150818041850.ga5...@wagner.pp.ru>. > > This patch implements following fuctionality: > > 1. It is allowed to specify several hosts in the connect string, either > in URL-style (separated by comma) or in param=value form (several host > parameters). > So what exactly would happen with this command: PGHOST=host1 psql -h host2 Or this one: PGHOST=host1 psql host=host2 What about service files? 2. Each host parameter can be accompanied with port specifier separated > by colon. Port, specified such way takes precedence of port parameter or > default port for this particular host only. > > 3. There is hostorder parameter with two possible valies 'sequential' > and 'random' (default sequential). 'parallel' hostorder described in the > proposal is not yet implemented in this version of patch. > > 4. In the URL-style connect string parameter loadBalanceHosts=true is > considered equal to 'hostorder=random' for compatibility with jdbc. > > 5. Added new parameter readonly=boolean. If this parameter is false (the > default) upon successful connection check is performed that backend is > not in the recovery state. If so, connection is not considered usable > and next host is tried. > > 6. Added new parameter falover_timeout. If no usable host is found and > this parameter is specified, hosts are retried cyclically until this > timeout expires. It gives some time for claster management software to > promote one of standbys to master if master fails. By default there is > no retries. > > Some implementation notes: > > 1. Field pghost in the PGconn structure now stores comma separated list > of hosts, which is parsed in the connectDBStart. So, expected results of > some tests in src/interfaces/libpq/test are changed. > trying postgresql://[::1]:12345/db -dbname='db' host='::1' port='12345' (inet) +dbname='db' host='[::1]:12345' (inet) Such a change doesn't look really nice to me. > 2. Url with colon but no port number after the host no more considered > valid. > We could live with that, but is there a good reason for backward compatibility break in this case? -- Alex
