Chapter 10 Storage and File Structure

Transcription

1 Chapter 10 Storage and File Structure Table of Contents z 2 ºÆ Ö c z Storage Media z Buffer Management z File Organization Chapter

2 1. 2 ºÆ Ö c z File Structure Selection Sequential, Indexed Sequential, Random z Mapping Relations to Files z Physical Record Format Design Fixed/Variable Length Record, Record Clustering z Index Selection Retrieval Time vs. Storage/Update Cost z Reorganization Performance Degradation with Time Chapter Storage Media 1. Storage Device Hierarchy 2. Magnetic Disk 3. RAID 4. Tertiary Storage Chapter

3 2.1 Storage Device Hierarchy Cache Main Memory Flash Memory Magnetic Disk Optical Disk Magnetic Tapes Chapter 10-4 Access Time vs. Capacity Tertiary Secondary Zip disk Floppy disk Main memory Cache Chapter

4 2.2 Magnetic Disk z Physical Characteristics of Disks Moving head vs. Fixed head Storing massive data Secondary storage device Random and sequential access Relatively fast z Access Time of Disks Seek Time Rotational Latency Data Transfer Rate Chapter 10-6 Moving-Head Mechanisms Chapter

5 Optimization of Disk Access z Disk Arm Scheduling FCFS, Shortest Seek Time First, Scan Algorithms z File Organization: Clustering z Nonvolatile Write Buffers NN Gë Òú Ÿ Battery-backed-up RAM (RAM disk), flash memory z Log Disk Log diskæ ör write: sequential (seek time ) DataÆ ör &S6 æ Ö ÓÒ Logr jÿr ë Chapter RAID z N Redundant Arrays of Inexpensive Disks Redundant Arrays of Independent Disks z Improvement of Reliability via Redundancy Mirroring or Shadowing Improvement in Performance via Parallelism Multiple small accessæ ör vn z Large AccessÆ ör Ç" Ž (Data Striping) Chapter

6 RAID Levels z RAID level 0: Non-Redundant Striping z RAID level 1: Mirrored Disks z RAID level 2: Memory Style Error Correcting Codes z RAID level 3: Bit Interleaved Parity z RAID level 4: Block Interleaved Parity z RAID level 5: Block Interleaved Distributed Parity z RAID level 6: P + Q Redundancy Chapter Tertiary Storage z Optical Disks Longer access time than magnetic disks {N: WORM, WORM jukeboxes, CD-RW, DVD z Magnetic Tapes Storing massive and archive data Sequential access only Slow speed {N: Digital Data Storage(DDS) Chapter

7 3. Buffer Management z Buffer Part of main memory to storage copies of disk blocks z Buffer Manager Subsystem responsible for the allocation of buffer space Requirements for buffer manager Replacement Strategy: LRU, FIFO, MRU Pinned Blocks: STEAL vs. STEAL Forced Output of Block: FORCE vs. FORCE Chapter Buffer ManagerN Ö c z Prefetching Patterns of future reference can be predicted by queries z Buffer Replacement Strategy IndexŽ Data DictionaryÆ ör Ö LRUö R;r ³? (þ: select * from student;) z Transaction Management Strategy Concurrency Control: Locking vs. Latching Recovery UNDO: STEAL, STEAL REDO: FORCE, FORCE Chapter

8 4. File Organization z Fixed Length Records z Variable Length Records z Mapping Relations to Files Chapter Fixed Length Records z b' type deposit = record branch-name : char (22); account-number : char (10); balance : real; end z Ë : bú Ÿj (î² 10.6) þjò æ N Ž Compaction (î² 10.7, 10.8) : Storage Efficiency List of deleted records (î² 10.9) Chapter

9 4.2 Variable Length Records z b' type deposit = record branch-name : char (22); account-info : array [1.. ] of record account-number : char (10); balance : real; end end z bú Byte-String Representation Fixed-Length Representation Chapter Byte-String Representation z Consecutive Bytes End-of-record ( ) r þjò ¾ Æ &S (î² 10.10) Difficult to handle grow and shrink z Slotted Page Structure Block Header # Entries Free Space End of Free Space Chapter

10 Fixed-Length Representation z Reserved Space Maximum record lengthr Ö (î² 10.12) Space :, But VjÚ. z Pointers List of fixed-length recordr Rú (î² 10.13) Access timej œú (due to frequent seek) Ö.j :ÒÚÆ ör Space : þž Anchor-block and Overflow-block bf (î² 10.14) Anchor Block: Ö.j :Ò ö Overflow Block: ö.j :Ò ö Chapter Mapping Relations to Files z Sequential File Organization One relation per file (î² 10.15, 10.16) Fixed length record Good for small database z Clustering File Organization Multiple relations in one file (î² 10.19, 10.20) Variable length records Good for certain operations, i.e Join Difficulty in sequential processing (î² 10.20) Chapter