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Flash Device Support for Database Management.

Flash Device Support for Database Management. . Authors: Philippe Bonnet, Luc Bouganim . In the 5th Biennial Conference on Innovative Data Research (CIDR) 2011. Presented by: Emery Mizero Computer Science Department February 23 rd , 2011. 0. Outline. Problem Statement

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Flash Device Support for Database Management.

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  1. Flash Device Support for Database Management. Authors: Philippe Bonnet, Luc Bouganim. In the 5th Biennial Conference on Innovative Data Research (CIDR) 2011 Presented by: Emery MizeroComputer Science Department February 23rd, 2011

  2. 0. Outline • Problem Statement • Flash Device characteristics • Minimal FTL vs. Bimodal FTL • Narrow Bimodal Flash Devices • Rich Bimodal Flash Devices • Conclusion • References

  3. 1. Problem Statement • Lack of consistent I/O behavior across Flash Device Models. • No Reference DBMS design for Flash • No Performance Model for Flash • Define how Flash devices should support DBMS • Provide DBMS a little more control over I/O behavior • How can Flash devices provide DBMS with guarantees over I/O behavior?

  4. 2. Flash Devices Characteristics • The Good * Great Performance (40 MB/s Reads, 10 MB/s Writes) * Low energy consumption * Potentially safe to power failure • The Bad * Write Granularity (page level) * Erase Before Writes (block level) * Sequential writes within a block * Limited Lifetime • The Flash Translation Layer (FTL) * out-of-place updates using log blocks * Garbage collection * Mapping between logical address space and Physical Flash space

  5. 3. Minimal vs. Bimodal FTL • Bimodal FTL + Optimal mapping for optimal blocks (DBMS guarantees to respect constraints C1-C3) + Other FTL mapping for non-optimal blocks (For other I/O patterns, the FTL enforces the constraints) * Sequential and semi-random write => optimal mapping • Minimal FTL + DBMS can issue I/O at page granularity. + DBMS rely on the Trim command to erase a flash block before write + DBMS can write flash page within a block in sequence. - DBMS cannot implement wear-leveling (guarantee the lifetime of a devices

  6. 3. Minimal vs. Bimodal FTL (…)

  7. 4. Narrow Bimodal Flash Devices • Interface is reduced to read/write/trim commands • The Flash exposes two constants:LBS (logical block size); LPS (logical page size) • Pages are written in the order that I/O are submitted. • Following information is maintained within the mapping in cache: • Physical Block ID • Current position with block • A bit flag for optimal mapping • Wear-leveling performed without knowledge of stored data • Non-optimized utilization of controller cache • Flash chip complexity managed at DBMS level

  8. 5. Rich Bimodal Flash Devices • From optimal block to optimal chunk => reduce the size of metadata.(explicit DBMS declaration of larger chunks to the Flash device) • Choosing highly erased blocks to store data with low erase frequency => Minimize block movements from FTL wear-leveling algorithms • Caching last written flash page into safe buffer; and written to flash when full (Append data structures: log records or table in append mode) • Caching payload: Only caching using useful data to be written thus avoiding caching of data that already exist in memory • Reading payload: Only transmitting useful data (within a page) from the chip to the controller and onto the host. • Nameless writes: Typically for temporary data, DBMS issues writes with no address. The FTL handles it and returns handle for future reference. • Reorganization for Free: the FTL wear-leveling mechanism involves the DBMS to do some of the work.

  9. 6. Conclusion • Flash should provide I/O guarantees. Why? • DBMS can devise stable and efficient IO management mechanisms. • What should the DB community do? • Guide the evolution of Flash devices so that guarantees can be enforced • Define the characteristics of the Flash Translation Layer that should be adopted on Flash devices across manufactures and Model.

  10. 7. Important References and Future work • Important References: • L. Bouganim, B. Jonsson, and P. Bonnet. uFLIP:UnderstandingFlash IO Patterns. In CIDR, 2009. • http://uflip.inria.fr/~uFLIP/ • Future work: • Explore the design space of Narrow Bimodal Flash devices for a optimized baseline design. • Following that would be to explore the design space of Rich Bimodal Flash devices.

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