Hi, How does Hedwig handles this scenario? Since only one of the hubs have the ownership of a topic, the same hub is able to serve both publish and subscribe requests concurrently. Is my understanding correct ?
Also, what is the purpose of ReadAheadCache class in Hedwig? Is it used somewhere for this concurrent read/write problem? -regards Amit ----- Original Message ---- From: Benjamin Reed <br...@yahoo-inc.com> To: zookeeper-user@hadoop.apache.org Sent: Fri, 22 October, 2010 11:09:07 AM Subject: Re: Is it possible to read/write a ledger concurrently currently program1 can read and write to an open ledger, but program2 must wait for the ledger to be closed before doing the read. the problem is that program2 needs to know the last valid entry in the ledger. (there may be entries that may not yet be valid.) for performance reasons, only program1 knows the end. so you need a way to propagate that information. we have talked about a way to push the last entry into the bookkeeper handle. flavio was working on it, but i don't think it has been implemented. ben On 10/21/2010 10:22 PM, amit jaiswal wrote: > Hi, > > In BookKeeper documentation, the sample program creates a ledger, writes some > entries and then *closes* the ledger. Then a client program opens the ledger, > and reads the entries from it. > > Is it possible for program1 to write to a ledger, and program2 to read from the > ledger at the same time. In BookKeeper code, if a client tries to read from a > ledger which is not being closed (as per its metadata in zk), then a recovery > process is started to check for consistency. > > Waiting for ledger to get closed can introduce lot of latency at the client > side. Can somebody explain this functionality? > > -regards > Amit
