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Re: slapd read-only slave replica

On Wednesday, 19 May 2010 22:02:57 DT Piotr Wadas wrote:
> Hello,
> Does it make any sens to enable indexing of any attribute on read-only
> slave syncrepl replica?

Whether or not indexes make sense is not dependant on whether the LDAP service 
is a provider or consumer or not, but dependent on what searches the LDAP 
service serves.

For example, if a provider only provides writes and changes to consumers, but 
no searches from clients, it only makes sense to index attributes required for 
replication. If a consumer is run purely for making offline backups of the 
master (e.g. by slapcat), and serves no searches, it may also make sense to 
index only replication attributes.

> I mean, isn't it just waste of resources, or,
> actually, is not a waste a resources at all, since replica is read-only
> and does not write anything anyway?

While a replica doesn't accept any changes from clients, it will write just as 
much as it's provider does on the same dataset, or it isn't doing a good job 
of replicating.

Typically, one normally configures the environment to direct read operations to 
slaves, so typically they have a higher read/write ratio, and it makes sense 
to have more indexes on slaves (the additional write IO for maintaining 
indexes is justified).