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Clouds mass over data warehousing

Started by dhilipkumar, Dec 15, 2008, 08:20 PM

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dhilipkumar



Suddenly the data warehousing sector seems to be hotting up. There's EMC's new competency centre and now Kognitio's in-memory data warehouse which threatens to brush server vendors aside if the idea gets adopted big time. How does that one work?

The story goes like this: Cluster lots of servers together in a shared-nothing architecture and use parallelising data-warehouse SW - WX2 in this case - to treat them as a single but very parallel resource. The servers all execute different threads of queries against the data that is stored in the servers' DRAM as an in-memory database. All other data, such as query results or a fraction of the data warehouse that is not in memory, is stored on disk - the servers' directly-attached disk and not in a networked disk resource such as a SAN or a NAS box.

Generally, with a disk-based data warehouse, only a fraction of the data is stored in memory, and query results executed against this are only looking at a data sample and not the full warehouse. Results from a full-warehouse query are statistically much more likely to be correct.

Roger Gaskell, the chief technology officer of Kognitio, says the firm is currently bidding for a 40TB data warehouse and its bid is less expensive than the installed DW system based on storage arrays and many servers. But how can 40TB memory-based system be cheaper?

It's cheaper in memory than on disk

The prospective customer, a large US business with a retail interest, currently has a 600TB data warehouse stored on a Fibre Channel-accessed modular drive-array resource, with queries processed by high-cost servers. Kognitio's bid is for 600 servers in a cluster - or, more accurately, a grid set-up - which collectively have 40TB of DRAM and 600TB of disk, but server direct-attached disk, and not modular arrays.

The servers are low-cost Dell or HP X86 servers and the cost of this set-up will be around $4,000,000, whereas the cost of the installed system was $5,000,000. Gaskell said that because the servers are so cheap, "The disk storage is almost free."

Gaskell told The Reg that the Kognitio system will be radically faster in answering queries - up to 80 times faster - than the disk-based system. The reason that the customer is looking to replace or augment the existing DW array-based system is because complex queries can now take up to four or more hours, and they'll be answered in three to six minutes on the in-memory Kognitio warehouse.

If this is true - that is, if the proposed system really is 80 times faster and a fifth less expensive - then it's a steal. Gaskell wouldn't identify the prospective customer because that company didn't want to upset its incumbent vendors. You can see why: Kognitio's technology renders DW use of storage arrays redundant. This customer still gets 600TB of disk but he'll be paying a much lower server-drive price rather than storage-array prices. Gaskell says, "You can get a terabyte of disk for about $400 on an HP rack-mount server."

Why not use flash storage instead of DRAM? Wouldn't it be cheaper still? Yes, it would, said Gaskell, but as a drive-array substitute it would only be two to three times faster than disk instead of 80 times faster, and the whole reason for going in-memory is to achieve the speed needed to get real-time response to queries.

Why not use a single big chunk of DRAM, like a TMS RamSan? "We have a shared-nothing architecture for reliability," said Gaskell. "If a server goes down we can work around that," meaning that if links to the RamSan or the RamSan itself goes down then, oops, your real-time response just went dead.

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