一道关于block尺寸计算的笔试题

Assume that a database designer plans to use the following SQL statement to create a relational

table Driver.

CREATE TABLE Driver (

Licence# NUMBER(8),

FName VARCHAR(30),

LName VARCHAR(30),

Address VARCHAR(50),

Phone# CHAR(10),

LicenceClass CHAR,

DOB DATE,

LicenceExpireDate DATE,

IssueState CHAR(3)) PCTFREE 20 TABLESPACE ATO;

Assume that size of disk data block is equal to 4K bytes.

1) Consider a model of data block explained in the course, assume a sample data block consists of a fixed size header (100 bytes), row directory (8 bytes per single entry), and data area. Find the total number of data blocks needed to store all 106 rows in the table Driver.

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2) Assume that tablespace ATO has free extents of 10MB each. Assume that the initial storage allocation should be large enough to accommodate information about 5*105 drivers.Propose a STORAGE clause for create table statement given above.   

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1. 一条记录的长度=8+30+30+50+10+1+8+8+3=148 bytes

   每条记录加8 bytes的指针区=148+8=156

   共106条记录 106*156=16536 bytes

   每个block的data区=(4*1024-100)*(1-0.2)=3196.8

   16536/3196=5.17=6块

   需要六个数据块

2. 需要存放的数据 5*105*156=81900 bytes

   需要的块数 81900/3196=25.63=27 块

   总大小 27*4=108K

  

CREATE TABLE Driver (

Licence# NUMBER(8),

FName VARCHAR(30),

LName VARCHAR(30),

Address VARCHAR(50),

Phone# CHAR(10),

LicenceClass CHAR,

DOB DATE,

LicenceExpireDate DATE,

IssueState CHAR(3))   

PCTFREE 20 TABLESPACE ATO

STORAGE(INITIAL 108K);