Advanced Programming in the UNIX® Environment

ptg10805159

782 ADatabase Library Chapter 20

1. Writenrecrecords to the database.


2. Read thenrecrecords back by key value.


3. Perform the following loopnrec× 5 times.
   a. Readarandom record.
   b. Every 37 times through the loop, delete a random record.
   c. Every11 times through the loop, insert a new recordand read the record
   back.
   d. Every 17 times through the loop, replace a random recordwith a new
   record. Every other one of these replacements is a recordwith the same size
   data; the alternate is a recordwith a longer data portion.


4. Delete all the records that this child wrote. Every time a record is deleted, ten
   random records arelooked up.

The number of operations performed on the database is counted by thecnt_xxx

variables in theDBstructure, which wereincremented in the functions. The number of

operations differs from one child to the next, since the random-number generator used

to select records is initialized in each child to the child’s process ID.Atypical count of

the operations performed in each child is shown in Figure20.6.

Calls tofcntl

(per operation)

Coarse-grained Fine-grained

locking locking

Operation

Operation

count

(nrec=2,000)

db_store,DB_INSERT, no empty record, appended 28 2,920

db_store,DB_INSERT,empty recordreused 2 4468

db_store,DB_REPLACE,different data length, appended 28405

db_store,DB_REPLACE,equal data length 22416

db_store,recordnot found 22 71

db_fetch,recordfound 2 23 2,873

db_fetch,recordnot found 22 2,966

db_delete,recordfound 2 43 ,388

db_delete,recordnot found 22422

Figure 20.6 Typical count of operations performed by each child

We performed about ten times morefetches than stores or deletions, which is probably

typical of many database applications.

Each child is performing these operations (fetching, storing, and deleting) only with

the records that the child wrote. The concurrency controls arebeing exercised because

all the children areoperating on the same database (albeit different records in the same

database). The total number of records in the database increases in proportion to the

number of children. (With one child,nrecrecords areoriginally written to the database.

With two children,nrec× 2 records areoriginally written, and so on.)

To test the concurrency provided by coarse-grained locking versus fine-grained

locking and to comparethe three types of locking (no locking, advisory locking, and