Sangam 19 - Successful Applications on Autonomous

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Connor McDonald
bit.ly/techguysong

The fundamentals of SQL processing
Connor McDonald
Database Advocate
Copyright © 2019 Oracle and/or its affiliates.

Slower and less secure in 45 minutes
Connor McDonald
Database Advocate
Copyright © 2019 Oracle and/or its affiliates.

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Me
youtube bit.ly/youtube-connor
blog connor-mcdonald.com
twitter @connor_mc_d
400+ posts mainly on database & development
250 technical videos, new uploads every week
rants and raves on tech and the world :-)

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etc...
facebook bit.ly/facebook-connor
linkedin bit.ly/linkedin-connor
instagram bit.ly/instagram-connor
slideshare bit.ly/slideshare-connor

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for successful applications...

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get | store results ... fast

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compile
execute
store/fetch results

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compile
execute
store/fetch results

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a little bit of history on servers ...

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you can't blame the server (anymore)

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so what's holding us back ?

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... not being able to do work

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cursorsdeclare
cursor C(p number) is
select * from DEPT
where DEPTNO = p;
begin
for rec in C loop
…
end loop;
end;
select *
from EMPLOYEE
where EMPNO > 1234;
delete from MY_TABLE;
drop table MY_TABLE;
begin
MY_PROCEDURE(1,2,3);
end;

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open
process
close
gimme some memory
do some stuff using that memory,
maybe access other memory
here's your memory back

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memory access = controlled access

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a quick primer on (database) memory

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limited resource
lots of people want it
concurrent access causes problems
it's a complex system

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SGA
protected by
1) get latch

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SGA
protected by
2) access memory

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SGA
protected by
3) release latch

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someone must wait ...
SGA
protected by

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spinning
can I have the latch ?

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"Errrr.... weren't we talking SQL?"

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Syntax
Validity
Optimization
Rowsourcing
Execution
(Fetch)
SQL> select *
2 frmo emp;
frmo emp
*
ERROR at line 2:
ORA-00923: FROM keyword not found where expected

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Syntax
Validity
Optimization
Rowsourcing
Execution
(Fetch)
SQL> select empnoo
2 from emp;
select empnoo
*
ERROR at line 1:
ORA-00904: invalid column name

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PLAN
-------------------------------------
SELECT STATEMENT
TABLE ACCESS BY INDEX ROWID EMP
INDEX RANGE SCAN EMP_PK
Syntax
Validity
Optimization
Rowsourcing
Execution
(Fetch)

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EMP_PK EMP
Syntax
Validity
Optimization
Rowsourcing
Execution
(Fetch)

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Syntax
Validity
Optimization
Rowsourcing
Execution
(Fetch)

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Syntax
Validity
Optimization
Rowsourcing
Execution
(Fetch)

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previously executed statements

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parse statement
already in library cache ?
reuse optimizer info
reuse row source info
select * from emp where empno = 123
syntactically, semantics OK

select surname, firstname from emp where empno = 123
select * from dept where deptno = 4567
select * from customer where locality = 17
select prno from property where reference = 'X123G'
select * from customer where locality = 256
select * from organisation where officer = 'OFF876'
select offender from crimes where crno = 247462
Two full parses avoided
library
cache

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select * from dept where dname = 'SALES'
probability of reuse low ?

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many queries are “nearly the same”

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binding
parse this...
now run it with ? = 123
now run it with ? = 456
select surname, firstname from emp where empno = ?

select * from dept where deptno = ?
select * from customer where locality = ?
select prno from property where reference = ?
select * from customer where locality = ?
select * from organisation where officer = ?
select offender from crimes where crno = ?
Five full parses avoided
library
cache

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demo
ParseDemo
ParseDemoBind

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"performance still looks ok"

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let's make it real
ParseDemo2 nn
ParseDemo2Bind nn

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building SQL by concatenation

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select ename
from emp
where empno = 6543
select ename
from emp
where empno = 6543
and 1=0
union all
select table_name
from all_tables
where table_name like '%SECURITY%'
select ename
from emp
where empno = 6543
and 1=0
union all
select username
from app_security
where ...

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#1 hacking app .... Google

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it takes 5 minutes to hack you

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data is stored in blocks | pages

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to read data, you read blocks...

SQL> select *
2 from EMP
3 where ...
/u01/my_data1.dat
memory

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but (database) memory access is complex

SQL> select *
2 from EMP
3 where …
SQL> update EMP
2 set …
3 where …
SQL> select *
2 from EMP
3 where …
SQL> insert into
2 EMP
3 values (…)
SQL> select *
2 from CUSTOMER
3 /
SQL> select max(EMP)
2 from DEPT
SQL> delete
2 from DEPT
3 /

• Get latch
• Search along list of blocks in memory
• Read block
• Extract row of interest
• Release latch
• Give row back to client
"fetch a row"

rs = stmt.executeQuery("...");
while(rs.next()) {
v1 = rs.getInt(1);
v2 = rs.getString(2);
...
}

rs = stmt.executeQuery("...");
while(rs.next()) {
v1 = rs.getInt(1);
v2 = rs.getString(2);
...
}
• Get latch
• Walk along list
• Get block
• Extract single row
• Release latch
• Give row back to client
• Get latch (again)
• Walk along list (again)
• Get block (again)
• Release latch (again)
• Give row back to client (again)
Row #1
Row #2
• Get latch (again)
• Walk along list (again)
• Get block (again)
• Release latch (again)
• Give row back to client (again)
Row #3

a better strategy.... “pinning”

"fetch a row"
• Get latch
• Walk along list
• Get block
• Pin the block
• Release latch
• Give row 1 back to client
…
• Give row n to client
• Get latch
• Walk along list
• Remove my pin on the block
• Release latch
“and ... I will need
several rows from
this block”

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how do you say
“I may want many rows” ?

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responsibility of the client

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all that data goes somewhere

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SQL> declare
. . .
9 begin
10 open c;
11 loop
12 fetch c
13 into r;
14 exit when c%notfound;
. . .
19 /
Elapsed: 00:01:11.72

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SQL> declare
. . .
9 begin
10 open c;
11
12 fetch c
13 bulk collect
14 into r;
15
. . .
19 /
Elapsed: 00:00:08.93

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SQL> select * from v$mystats
2 where name like '%pga%'
3 /
NAME VALUE
------------------------------ ----------
session pga memory 501534672
session pga memory max 501534672

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law of diminishing returns

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SQL> declare
. . .
9 begin
10 open c;
11 loop
12 fetch c
13 bulk collect
14 into r limit 100;
15 exit when c%notfound;
. . .
19 /
Elapsed: 00:00:08.17
NAME VALUE
------------------------------ ----------
session pga memory 625912
session pga memory max 625912

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SQL> declare
. . .
9 begin
10 for i in c loop
12 ...
16 end loop;
17 end;
18 /
Elapsed: 00:00:08.21

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think blocks not rows
when appropriate

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demo
InsertDemo3
InsertDemo4 nn

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for slow and insecure applications...

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no binding, no SQL reuse, no pinning

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... hence fast, secure applications

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... always bind user input

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... use pinning/array processing

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Thank you
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Sangam 19 - Successful Applications on Autonomous

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