CS 457/557, assignment 2

Due Friday, 26 January, 2018

RAID recovery

After a power failure, there is a recovery process that we shal study in Chapter 17. During this process, any recently written block will need to be re-read, and probably modified. It can happen that one such block was only half written, so neither the old nor new version can be read.

Assuming there are 5 RAID disks, restore this block (the first 10 bits) from the other 4:

      1 1 1 1 1  0 0 0 0 0
      1 1 0 0 1  1 0 0 1 0
      1 0 1 0 1  0 1 0 1 1
      1 1 1 0 0  0 1 1 0 1

new:

Record and Block layout

Similar to (but not) Exercise 13.5.1 (p. 593), "dereferenced"

Suppose a fixed-length record has the following fields in this order:

A real of 8 bytes,
A character string of length 17, [ char(17) or varchar(16) ]
A single byte, and
an SQL date (stored as characters, for example 2018-01-26 ).

Each record also has a record header, consisting of two 4-byte pointers and a character.

1. Calculate the record length of such a record for these 2 situations regarding field alignment:

Fields can start an any byte
Fields must start at a byte that is a multiple of 4

2. How many records can we fit in a block 16,384 bytes long (16K bytes), for each field alignment (a. & b.),
where there is also a block header consisting of three 8-byte integers.

Record length as in 1. a.
Record length as in 1. b.

Submit on paper, or see How to submit in Assignment 1.

Lin Jensen. Back to course