* Marko Kreen <[EMAIL PROTECTED]> [080529 12:27]: > I don't think thats a problem. If the user runs its server at the > limit of write-bandwidth, thats its problem. > > IOW, with synchronous replication, we _want_ the server to lag behind > slaves. > > About the single-threading problem - afaik, the replay is mostly I/O bound > so threading would not buy you much.
Right - the problem is that the master has N>1 backends working away, preloading the modified heap pages into shared buffers, where they are modified w/ WAL. This means the kernel/controller has man read-requests in flight at a time as the modifies/writes chug along. The slave has to read/modify/write every buffer, one at a time, as WAL arrives, meaning there is ever only 1 IO request in flight at a time. So the server as a queue of many parallel reads going on, the slave has a set of sequential random reads going on. a. -- Aidan Van Dyk Create like a god, [EMAIL PROTECTED] command like a king, http://www.highrise.ca/ work like a slave.
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