I'm pretty sure it's over HTTP, although I don't know the details of the requests/responses.

The slave will download any index files that have changed on master. A Solr index is split up amongst a number of seperate files on disk. There's no way for slave to get a delta beyond getting a complete index file if and only if it's changed --- index files that haven't changed won't be downloaded, index files that are new will be downloaded. (I think 'new' is basically the same as 'changed', I am not sure if index files are ever actually changed, rather than new ones being created and old ones (after a merge/optimize operation) being deleted).

One side effect of this is if an 'optimize' is run on master, then typically all index files will have to be downloaded. (Likewise if an optimize is run on slave, next replication all index files will be downloaded. There's generally no good reason to run an optimize on slave, or otherwise do anything to change the index at all on slave).

On 5/25/2011 1:11 PM, antoniosi wrote:
Hi,

I am just curious what is the communication protocol that a slave node get
the index update from the master node in a replication settings? Is it
through TCP? I assume it only gets the delta?

Thanks very much in advance.


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