Aaron, Thanks for your reply. Here are the answers to questions you had asked:
I am trying to read all the rows which have a particular TimeStamp. In my data base, there are 500 K entries for a particular TimeStamp. That means about 40 MB of data. The query returns fine if I request for lesser number of entries (takes 15 seconds for returning 20K records). However, as I increase the limit on number of entries, the response begins to slow down. It results in TimedOutException. Isn't it the case that all the data for a partitionID is stored sequentially in disk? If that is so, then why does fetching this data take such a long amount of time? If disk throughput is 40 MB/s, then assuming sequential reads, the response should come pretty quickly. Is it not the case that the data I am trying to fetch would be sequentially stored? If it is stored sequentially, why does C* take so much time to return the records? And if data is stored sequentially, is there any alternative that would allow me to fetch all the records quickly (by sequential disk fetch)? Thanks Pushkar -----Original Message----- From: aaron morton [mailto:aa...@thelastpickle.com] Sent: 19 March 2013 13:11 To: user@cassandra.apache.org Subject: Re: Unable to fetch large amount of rows > I have 1000 timestamps, and for each timestamp, I have 500K different MACAddress. So you are trying to read about 2 million columns ? 500K MACAddresses each with 3 other columns? > When I run the following query, I get RPC Timeout exceptions: What is the exception? Is it a client side socket timeout or a server side TimedOutException ? If my understanding is correct then try reading fewer columns and/or check the server side for logs. It sounds like you are trying to read too much though. Cheers ----------------- Aaron Morton Freelance Cassandra Consultant New Zealand @aaronmorton http://www.thelastpickle.com On 19/03/2013, at 3:51 AM, Pushkar Prasad <pushkar.pra...@airtightnetworks.net> wrote: > Hi, > > I have following schema: > > TimeStamp > MACAddress > Data Transfer > Data Rate > LocationID > > PKEY is (TimeStamp, MACAddress). That means partitioning is on TimeStamp, and data is ordered by MACAddress, and stored together physically (let me know if my understanding is wrong). I have 1000 timestamps, and for each timestamp, I have 500K different MACAddress. > > When I run the following query, I get RPC Timeout exceptions: > > > Select * from db_table where Timestamp='...' > > From my understanding, this should give all the rows with just one disk seek, as all the records for a particular timeStamp. This should be very quick, however, clearly, that doesn't seem to be the case. Is there something I am missing here? Your help would be greatly appreciated. > > Thanks > PP
