- Service:
- Service =
an activity that
is useful/helpful to
many users
- A service is provide by making a request to a well-known location
Example:
- Emergency service to
request
urgent help
- The emergency service is requested through telephone at the well-known number: 911
- Service =
an activity that
is useful/helpful to
many users
- How to
provide the 911 (emergency) service:
- We staff
a call center with
service providers
that work
24/7
(= 24 hours a day and 7 days a week):
- A call to
911 is
routed to
a service provider
in the 911 center:
- Your call/request will
be serviced by
a service provider when
your request is
received:
- We staff
a call center with
service providers
that work
24/7
(= 24 hours a day and 7 days a week):
- How to
provide a
service on the
Internet:
- Run a
server program on
a computer
(e.g.:
holland.mathcs.emory.edu)
The server program must run 24/7 (i.e.: always !!!)
- A user that want
to use the
service run a
(special) client program that
can make a request to the
server program:
- The server program
will process the
request and
send a
response back
to the client program:
The response will contain the result of the request made by the client program
- Run a
server program on
a computer
(e.g.:
holland.mathcs.emory.edu)
- Architecture to provide
database service:
Explanation:
- On a specifical machine
(in our case:
holland.mathcs.emory.edu),
we run the
MySQL server
that:
- provides the database service for users (students)
- Users (students !) execute
a client program
(cs377-sql)
that:
- Send
request (= queries) to
the mySQL server running on
holland.mathcs.emory.edu
- And receive (and display) the reply (= query result) from the mySQL server
- Send
request (= queries) to
the mySQL server running on
holland.mathcs.emory.edu
- On a specifical machine
(in our case:
holland.mathcs.emory.edu),
we run the
MySQL server
that:
- Detailed interaction:
- First,
the client program
establish a
network connection
to
the mySQL server
on holland.mathcs.emory.edu:
- Then the
client program sends an
SQL command
to the mySQL server
for execution:
This is the request !!!!
- In response, the
mySQL server sends
back the
result set (tuples)
to the client:
This is the reply !!!!
- First,
the client program
establish a
network connection
to
the mySQL server
on holland.mathcs.emory.edu:
- How to see the
mySQL "server" that is
running on holland:
1. ssh -X holland 2. Run: ps -e | grep mysql // program is called mysqld The first number is the "process ID (PID)" of the mySQL daemon 3. Run: ps -q PID -l