454.3-09.Hardware

454.3-09.Hardware - Database Systems II Secondary Storage...

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CMPT 454, Simon Fraser University, Fall 2009, Martin Ester 29 Database Systems II Secondary Storage CMPT 454, Simon Fraser University, Fall 2009, Martin Ester 30 The Memory Hierarchy Disk Tertiary Storage: Tape, Network Backup Main Memory L1/L2-Cache (256KB 4MB) Disk-Cache (2 16MB) 300 MB/s (SATA-300) 16 GB/s (64bit@2GHz) 6,400 MB/s 12,800 MB/s (DDR2, dual channel, 800MHz) CPU-to-L1-Cache: ~5 cycles initial latency, then “burst” mode CPU Virtual Memory File System CPU-to-Main-Memory: ~200 cycles latency 3,200 MB/s (DDR-SDRAM @200MHz) Swapping, Main-memory DBMS’s
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CMPT 454, Simon Fraser University, Fall 2009, Martin Ester 31 The Memory Hierarchy Cache Data and instructions in cache when needed by CPU. On-board (L1) cache on same chip as CPU, L2 cache on separate chip. Capacity ~ 1MB, access time a few nanoseconds. Main memory All active programs and data need to be in main memory. Capacity ~ 1 GB, access time 10-100 nanoseconds. CMPT 454, Simon Fraser University, Fall 2009, Martin Ester 32 The Memory Hierarchy Secondary storage Secondary storage is used for permanent storage of large amounts of data, typically a magnetic disk. Capacity up to 1 TB, access time ~ 10 milliseconds. Tertiary storage To store data collections that do not fit onto secondary storage, e.g. magnetic tapes or optical disks. Capacity ~ 1 PB, access time seconds / minutes.
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CMPT 454, Simon Fraser University, Fall 2009, Martin Ester 33 The Memory Hierarchy Trade-off The larger the capacity of a storage device, the slower the access (and vice versa). A volatile storage device forgets its contents when power is switched off, a n on-volatile device remembers its content. Secondary storage and tertiary storage is non- volatile, all others are volatile. DBS needs non-volatile (secondary) storage devices to store data permanently. CMPT 454, Simon Fraser University, Fall 2009, Martin Ester 34 The Memory Hierarchy RAM (main memory) for subset of database used by current transactions. Disk to store current version of entire database (secondary storage). Tapes for archiving older versions of the database (tertiary storage).
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CMPT 454, Simon Fraser University, Fall 2009, Martin Ester 35 The Memory Hierarchy Typically programs are executed in virtual memory of size equal to the address space of the processor. Virtual memory is managed by the operating system, which keeps the most relevant part in the main memory and the rest on disk. A DBS manages the data itself and does not rely on the virtual memory. However, main memory DBS do manage their data through virtual memory. CMPT 454, Simon Fraser University, Fall 2009, Martin Ester 36 Moore’s Law Gordon Moore in 1965 observed that the density of integrated circuits (i.e., number of transistors per unit) increased at an exponential rate, thus roughly doubles every 18 months . Parameters that follow Moore‘s law:
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454.3-09.Hardware - Database Systems II Secondary Storage...

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