Re: Transaction Snapshots and Hot Standby
От | Simon Riggs |
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Тема | Re: Transaction Snapshots and Hot Standby |
Дата | |
Msg-id | 1221209146.3913.948.camel@ebony.2ndQuadrant обсуждение исходный текст |
Ответ на | Re: Transaction Snapshots and Hot Standby (Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>) |
Ответы |
Re: Transaction Snapshots and Hot Standby
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Список | pgsql-hackers |
On Thu, 2008-09-11 at 15:42 +0300, Heikki Linnakangas wrote: > Gregory Stark wrote: > > b) vacuum on the server which cleans up a tuple the slave has in scope has to > > block WAL reply on the slave (which I suppose defeats the purpose of having > > a live standby for users concerned more with fail-over latency). > > One problem with this, BTW, is that if there's a continuous stream of > medium-length transaction in the slave, each new snapshot taken will > prevent progress in the WAL replay, so the WAL replay will advance in > "baby steps", and can fall behind indefinitely. As soon as there's a > moment that there's no active snapshot, it can catch up, but if the > slave is seriously busy, that might never happen. It should be possible to do mixed mode. Stall WAL apply for up to X seconds, then cancel queries. Some people may want X=0 or low, others might find X = very high acceptable (Merlin et al). -- Simon Riggs www.2ndQuadrant.comPostgreSQL Training, Services and Support
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