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@ -1,4 +1,4 @@ |
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<!-- $PostgreSQL: pgsql/doc/src/sgml/high-availability.sgml,v 1.73 2010/06/11 10:13:08 heikki Exp $ --> |
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<!-- $PostgreSQL: pgsql/doc/src/sgml/high-availability.sgml,v 1.74 2010/06/22 02:57:50 rhaas Exp $ --> |
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<chapter id="high-availability"> |
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<title>High Availability, Load Balancing, and Replication</title> |
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@ -1330,7 +1330,7 @@ if (!triggered) |
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</listitem> |
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<listitem> |
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<para> |
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LISTEN, UNLISTEN, NOTIFY |
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<command>LISTEN</>, <command>UNLISTEN</>, <command>NOTIFY</> |
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</para> |
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</listitem> |
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</itemizedlist> |
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@ -1437,14 +1437,14 @@ if (!triggered) |
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Some WAL redo actions will be for <acronym>DDL</> execution. These DDL |
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actions are replaying changes that have already committed on the primary |
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node, so they must not fail on the standby node. These DDL locks take |
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priority and will automatically *cancel* any read-only transactions that |
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get in their way, after a grace period. This is similar to the possibility |
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of being canceled by the deadlock detector. But in this case, the standby |
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recovery process always wins, since the replayed actions must not fail. |
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This also ensures that replication does not fall behind while waiting for a |
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query to complete. This prioritization presumes that the standby exists |
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primarily for high availability, and that adjusting the grace period |
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will allow a sufficient guard against unexpected cancellation. |
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priority and will automatically <emphasis>cancel</> any read-only |
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transactions that get in their way, after a grace period. This is similar |
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to the possibility of being canceled by the deadlock detector. But in this |
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case, the standby recovery process always wins, since the replayed actions |
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must not fail. This also ensures that replication does not fall behind |
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while waiting for a query to complete. This prioritization presumes that |
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the standby exists primarily for high availability, and that adjusting the |
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grace period will allow a sufficient guard against unexpected cancellation. |
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</para> |
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<para> |
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