APEX Connect 2019 - successful application development

... successful application development

Copyright © 2018, Oracle and/or its affiliates. All rights reserved.
Connor McDonald

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5

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Getting in touch is easy...
connor-mcdonald.com
https://linktr.ee/connor

8https://asktom.oracle.com

https://asktom.oracle.com/officehours

200 hours free access so far
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assumptions
1. You roughly know databases (tables and columns)
2. You can write a SQL statement

before we begin

recommended reading

docs.oracle.com

its free !

Concepts guide
http://bit.ly/oraconcepts

better than lots of current people

Application Developers guide
http://bit.ly/oradevdoc

Part 1
SQL processing

some controversy to start...

here's the problem...
22

... it's us

a little digression on servers

a little bit of history ...

(not too) long ago

FSB = "front side bus"
28

any access to ... anything

CPU capped

hypertransport

memory access direct from CPU
35

"why do I care?"

you can't blame the server
39

if you can't get that performance ...

... it's you

all have their place...

"The sooner your company admits that you are not
Google, the sooner you can get down to some real work"
- Ted Dziuba
47

so what's holding you back ?

It all comes down to...

too much work or ...

... not being able to do work
51

this part ...

... how to avoid work when processing SQL

terminology
54

cursors
declare
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;

all of them !

3 phases

open
process
close
gimme some memory
do some stuff using that memory,
probably access other memory
here's your memory back
58

memory access = controlled access

a quick primer on (database) memory

64
limited resource
lots of people want it
concurrent access causes problems
it's a complex system

SGA
protected by
2) access memory

SGA
protected by
3) release latch

SGA
protected by
someone must wait ...

spinning
can I have the latch ?
76

its importance to Oracle

early Oracle

2000 times !
(_spin_count)
87

Zzzzzzzzzz....

nowadays...
yield
mutex
posting
Good reading: http://andreynikolaev.wordpress.com/
CAS

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

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
92

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

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

EMP_PK EMP
Syntax
Validity
Optimization
Rowsourcing
Execution
(Fetch)

Syntax
Validity
Optimization
Rowsourcing
Execution
(Fetch)
96

Syntax
Validity
Optimization
Rowsourcing
Execution
(Fetch)

impossible to avoid ?

library cache

previously executed statements
104

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

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

some queries are “nearly the same”
108

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

let's make it real
ParseDemo2 nn
ParseDemo2Bind nn

select pk from parse_demo where pk = 17

it takes 5 minutes to hack you

while we are talking binding

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

still some parsing to do
127

Syntax
Validity
Optimization
Rowsourcing
Execution
(Fetch)
Hard
Parse
Soft
Parse
foundnot found
in lib cache

scott@mydb> select *
2 from EMP
3 where EMPNO = :b1
mike@mydb> select *
2 from EMP
3 where EMPNO = :b1
SQL> desc mike.emp
Name Null? Type
----------------- -------- ------------
EMPNO NOT NULL NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)

(even soft) parsing =
memory access =
latching

can we do better ?

recall

open
process
close
gimme some memory
do some stuff using that memory,
probably access other memory
here's your memory back
133

your SQL is always shareable
library cache
select *
from emp

your cursor points to it
library cache
select *
from emp
cursor
135

close cursor = lose pointer
library cache
select *
from emp
cursor

next time we parse
soft parse

impossible to avoid ?
138

what if we don't close the cursor

emplist(String[] args) {
if "first time I'm using this" {
else
"reset the pointer, re-execute"
}
library cache
select *
from emp
cursor 1
select *
from dept
cursor 2
select *
from emp
where ...
cursor 3
pstmt_all_emp =
con.prepareStatement("select * from emp");

don’t close the cursorhang on to the memoryremember what cursors we’ve usedreuse whenever possibledon’t exhaust memorydon’t allow invalid cursor reuse

sounds complicated ...

a free solution exists

plsql

create procedure MY_PROC is
begin
select empno, ename, ...
into …
from emp
where empno = my_plsql_variable
...
end;

static SQL in stored PLSQL
automatically uses bind variables
hold’s cursors open
(even if you close)

better cursor caching

procedure MY_PROC is
cursor c_emp is
select * from emp;
begin
open c_emp;
fetch c_emp
into …;
close c_emp;
end;
select * from emp
procedure MY_PROC is
begin
select *
into …
from dept
where …
end;
select * from dept …

summary

avoid parsing costs
for high frequency SQL

binding

using PLSQL is gold

if time permits ....

156
"Readers don’t block writers"
"Writers don't block readers"

157
Maximum concurrency…
… very few locking worries

158
lack of understanding

160
some revision / fundamentals

SQL> update EMP
2 set SAL = SAL * 1.10
3 /
14 rows updated.
SQL> rollback;
Rollback complete.
how ?
161

SQL> update EMP
2 set SAL = SAL * 1.10
3 / undo header
smith $1,0001
block 2754
jones $9002
brown $1,5003
wells $2,0004
wilson $1,0005
block 2754, row 1,
sal $1000
block 2754, row 2,
sal $900
block 2754, row 3,
sal $1500
block 2754, row 4,
sal $2000
uba 5
5
$1,100
$990
$1,650
$2,200
uba 5.1uba 5.2
163

SQL> rollback;
undo header
smith $1,0001
block 2754
jones $9002
brown $1,5003
wells $2,0004
wilson $1,0005
block 2754, row 1,
sal $1000
block 2754, row 2,
sal $900
block 2754, row 3,
sal $1500
block 2754, row 4,
sal $2000
uba 5
5
$1,100
$990
$1,650
$2,200
uba 5.1uba 5.2

we can use this stuff for queries!
(Oracle version 4)
166

select * from emp
where hiredate > '01/01/2004'
update emp set …
where empno = 1234;
Block 3217
"I need block 3217…
… as it was at 9:00"
9:00
9:03
9:05
session 1 session 2
...and time = scn

System Change Number
(the block “timestamp”)

Block 3217
SCN 4567192
SCN 4567234
“9am”
“9:03am”
session 1
170

Session 1
Request
Block 3217,
SCN 4567192
Block 3217,
SCN 4567234
"ABC"
Block 3217,
SCN 4567003,
change ABC => XYZ
undo segment block(s)
No good..too new
take a copy of the block
Locate
apply undo
Block 3217,
SCN 4567234
"ABC"
Block 3217,
SCN 4567234
"ABC"
Block 3217,
SCN 4567003
"XYZ"
Block 3217,
SCN 4567003
"XYZ"
Session 2
update emp
set ename = "ABC"
where empno = 1234;
commit;
Done !
173

“I’m a developer…
I just write SQL ...
…who cares about all that?”

“every hour,
populate data warehouse,
copy of OLTP data”
EMP DWEMP
readcon1/readcon2

DIY data integrity
... true story
181

Manufacturer
Product
alter table add primary key
alter table add foreign key
“ensure that every
product corresponds to
a valid manufacturer”

create or replace
trigger PROD_MAN_CHECK
before insert or update on PRODUCT
for each row
declare
l_man_id number;
begin
select man_id
into l_man_id
from manufacturer
where man_id = :new.man_id;
exception
when no_data_found then
raise_application_error(-20000,
'Manufacturer is not valid');
end;

create or replace
trigger MAN_PROD_CHECK
before delete on MANUFACTURERS
for each row
declare
l_prd_cnt number;
begin
select count(*)
into l_prd_cnt
from product
where prd_id = :old.prd_id;
if l_prd_cnt > 0 then
raise_application_error(-20001,
'Manufacturer in use by product records');
end if;
end;

SQL> insert into PRODUCT (...,MAN_ID,...)
2 values (...,100, ...);
1 row created.
SQL> insert into PRODUCT (...,MAN_ID,...)
2 values (...,101,...);
ERROR at line 1:
ORA-20000: Manufacturer is not valid
SQL> delete from MANUFACTURER
2 where man_id = 5768;
ERROR at line 1:
ORA-20001: Manufacturer in use by product records

An unexpected error has
occurred. Manufacturer
record not found

SQL> select count(*)
2 from
3 ( select man_id from PRODUCT
4 minus
5 select man_id from MANUFACTURER )
6 /
COUNT(*)
----------
86
189

data integrity in code = no data integrity

Time
create PRD with MAN=7
Trigger fires
- does MAN=7 exist?
- "Yes"
- OK
delete MAN=7
Trigger fires
- any PRD with MAN=7
- "No" (not yet)
- OK
commit
commit

data validity seems simple…
"look up X before allowing Y"
192

referential integrity is complex
read consistency,
blocking / locking

beware the module specification
"When creating a product...
validate registration date – ensure not in the future,
validate …
validate …
validate manufacturer ID – must exist in Manufacturer table"

“I’m a developer…
…who cares about all that?”
part 2

“All that stuff is a DBA issue,
I just want my code to run fast”
demo3

summary revisited

use binding for SQL

use SQL wherever possible

use PLSQL to run your SQL

Thanks for coming!
connor-mcdonald.com
https://linktr.ee/connor
APEX Connect
SQL Tuning 101
PL/SQL Performance 101

APEX Connect 2019 - successful application development

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