Need to purge applied log from arch_replicate directory

Dear all,

I am test postgres streaming replication under 9.0.4. The master and
slave have been replicated smoothly. In master, I have a directory
"/path/to/arch_replicate/" to used by slave to access and apply the
logs. The arch_replicate directory has been growing without purging any
applied logs. What is the best way to manage the logs to save the disk
space? I also found my postgres does not have pg_archivecleanup
utility. Where do I find this utility? How do I use this utility?
Your help would be greatly appreciated.

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Best regards,

Alex Lai