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docs: Improve A?synchronous Multimaster Replication descr. 

The docs for sync and async multimaster replication were unclear about
when to use it, and when it has benefits;  this change clarifies that.

Reported-by: juha-pekka.eloranta@reaktor.fi

Discussion: https://postgr.es/m/156856543824.1274.12180817186798859836@wrigleys.postgresql.org

Backpatch-through: 9.4
This commit is contained in:
Bruce Momjian 2019-10-07 18:06:08 -04:00
parent cae078f3f9
commit 47eec34e46
1 changed files with 4 additions and 4 deletions
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8
doc/src/sgml/high-availability.sgml
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@ -237,7 +237,8 @@ protocol to make nodes agree on a serializable transactional order.
<listitem> <listitem>
<para> <para>
For servers that are not regularly connected, like laptops or For servers that are not regularly connected or have slow
communication links, like laptops or
remote servers, keeping data consistent among servers is a remote servers, keeping data consistent among servers is a
challenge. Using asynchronous multimaster replication, each challenge. Using asynchronous multimaster replication, each
server works independently, and periodically communicates with server works independently, and periodically communicates with
@ -256,9 +257,8 @@ protocol to make nodes agree on a serializable transactional order.
In synchronous multimaster replication, each server can accept In synchronous multimaster replication, each server can accept
write requests, and modified data is transmitted from the write requests, and modified data is transmitted from the
original server to every other server before each transaction original server to every other server before each transaction
commits. Heavy write activity can cause excessive locking, commits. Heavy write activity can cause excessive locking and
leading to poor performance. In fact, write performance is commit delays, leading to poor performance. Read requests can
often worse than that of a single server. Read requests can
be sent to any server. Some implementations use shared disk be sent to any server. Some implementations use shared disk
to reduce the communication overhead. Synchronous multimaster to reduce the communication overhead. Synchronous multimaster
replication is best for mostly read workloads, though its big replication is best for mostly read workloads, though its big