From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <43644094f7203744e1cc2345ccebb26a@plan9.bell-labs.com> To: 9fans@cse.psu.edu Subject: Re: [9fans] QTCTL? Date: Thu, 1 Nov 2007 12:17:49 -0400 From: Sape Mullender In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Topicbox-Message-UUID: e3729e94-ead2-11e9-9d60-3106f5b1d025 > In the case of read cache (which is probably going to be used more > often than write-cache), the client needs to send two RPC every time > a writer modifies the cached file. What if Rlease doesn't necessary > break the lease, but have an option (negotiated in Tcache) to let the > client know that the file is changed without breaking the lease. That breaks single-copy semantics: A client may have acted on data after it had been changed by somebody else. Say, A and B are sharing the file. B has a read-lease on the file, A obtains a write lease, modifies the file and sends a message to A to read what was changed. A reads the file (which is still in the cache and has not been updated). Meanwhile, just after B obtained the write lease, the server notifies A that the lease is expiring early, but this message travels slowly and doesn't arrive until the whole exchange is over. Sape