Storage and File Structure

Transcription

1 CSL 451 Introduction to Database Systems Storage and File Structure Department of Computer Science and Engineering Indian Institute of Technology Ropar Narayanan (CK) Chatapuram Krishnan!

2 Summary Physical Storage Media cache - main memory - flash storage - magnetic disk - optical storage - tapes Performance measures of disks access time seek time average seek time rotational latency time average latency data transfer rate mean time to failure Disk-Block access block sequential access random access buffering, read-ahead, scheduling, file organization. Flash Storage RAID mirroring mean time to repair mean time to data loss striping bit-level striping block-level striping RAID levels 0, 1, 2, 3, 4 and 5 2!

3 RAID Levels 3!

4 Summary Physical Storage Media cache - main memory - flash storage - magnetic disk - optical storage - tapes Performance measures of disks access time seek time average seek time rotational latency time average latency data transfer rate mean time to failure Disk-Block access block sequential access random access buffering, read-ahead, scheduling, file organization. Flash Storage RAID mirroring mean time to repair mean time to data loss striping bit-level striping block-level striping RAID levels 0, 1, 2, 3, 4 and 5 scrubbing File Organization blocks fixed length records free list variable length records slotted page structure 4!

5 Slotted Page Structure Block Header Records Size Location # Entries Free Space End of Free Space 5!

6 Summary Physical Storage Media cache - main memory - flash storage - magnetic disk - optical storage - tapes Performance measures of disks access time seek time average seek time rotational latency time average latency data transfer rate mean time to failure Disk-Block access block sequential access random access buffering, read-ahead, scheduling, file organization. Flash Storage RAID mirroring mean time to repair mean time to data loss striping bit-level striping block-level striping RAID levels 0, 1, 2, 3, 4 and 5 scrubbing File Organization blocks fixed length records free list variable length records slotted page structure record organization heap, sequential, hashing Database Buffer buffer manager 6!

7 List the advantages and disadvantages of RAID-3 over RAID-1 7!

8 Comment on the performance of RAID-4 8!

9 10.1 Consider the data and parity-block arrangement on four disks. The B i s represent data blocks; the P i s represent parity blocks. Parity block P i is the parity block for data blocks B 4i-3 to B 4i. What, if any problem might this arrangement present? 9!

10 10.3 A power failure that occurs while a disk block is being written could result in the block being only partially written. Assume that partially written blocks can be detected. An atomic block write is one where either the disk block is fully written or nothing is written (i.e., there are not partial writes). Suggest schemes for getting the effect of atomic block writes for RAID level 1 (mirroring). Your schemes should involve work on recovery from failure. 10!

11 10.2.a Flash Storage: How is the flash translation table, which is used to map logical page numbers to physical numbers, created in memory? 11!

12 10.2.b Flash Storage: Suppose you have a 64GB flash storage system, with a 4096 byte page size. How big would the flash translation table be, assuming each page has a 32 bit address, and the table is stored as an array. 12!

13 10.2.c Flash Storage: Suggest how to reduce the size of the translation table if very often long ranges of consecutive logical page numbers are mapped to consecutive physical page numbers 13!

14 10.11 How does the remapping of bad sectors by disk controllers affect the data retrieval rates? 14!

15 10.20 If you have data that should not be lost on disk failure, and the data are write intensive, how would you store the data? 15!

16 10.4 Consider the deletion of record 5 from the following file. Compare the relative merits of the following techniques for implementing the deletion a. Move record 6 to the space occupied by record 5, and move record 7 to the space occupied by record 6. b. Move record 7 to the space occupied by record 5. c. Mark record 5 as deleted, and move no records. 16!

17 10.5 Show the structure of the file after each of the following steps a. Insert(24556, Turnamian, Finance, 98000) b. Delete record 2 c. Insert(34556, Thompson, Music, 67000) 17!

18 10.7 Consider the following bitmap technique for tracking free space in a file. For each block in the file, two bits are maintained in the bitmap. If the block is between 0 and 30 percent full the bits are 00, between 30 and 60 percent the bits are 01, between 60 and 90 percent the bits are 10, and above 90 percent the bits are 11. Such bitmaps can be kept in main memory even for quite large files. a. Describe how to keep the bitmap up to date on record insertions and deletions. b. Outline the benefit of the bitmap technique over free lists in searching for free space and in updating free space information. 18!

19 10.13 What is scrubbing, in the context of RAID systems, and why is scrubbing important? 19!

20 10.15 Explain why the allocation of related records to blocks affects database-system performance significantly? 20!

21 10.9 Give an example of a relational-algebra expression and a query-processing strategy where MRU is preferable to LRU 21!