dev-21: optimising your abl for performance making your code go faster gus björklund wizard,...

DEV-21: Optimising Your ABL For Performance

Making your code go faster

Gus BjörklundWizard, Progress Software Corporation

© 2007 Progress Software Corporation2 DEV-21:Optimizing Your ABL for Performance

"More computing sins are committed in the name of efficiency (without necessarily achieving it) than for any other single reason - including blind stupidity.”

W.A. Wulf


“The First Rule of Program Optimisation: Don't do it.

The Second Rule of Program Optimisation (for experts only!): Don't do it yet.”

Michael A. Jackson


Things

Why optimise When to optimise What to optimise How to optimise


Why optimise


Why (not) optimise

Optimising is work Processors get faster and faster Databases get faster and faster Disks get faster and faster (and bigger) Memory gets faster and faster (and bigger)

Why spend time optimising when we don’t need to,and you just warned me not to do it ??


Why optimise

Performance is never good enough Can’t ask customer to buy a new machine Faster machines won’t solve every problem No machine bigger than the biggest Smaller machines cost less than big ones You can put more users on a machine Better performance improves customer

satisfaction

But: Don’t do work that is not needed!


When to optimise


When to optimise

After you have• spent enough time thinking

• chosen the right algorithms

• working code

• measured performance of your application

• determined you have a problem


What to optimise


The Pareto principle

80 % of the consequences stem from 20 % of the causes


"We should forget about small efficiencies, say about 97% of the time: premature optimisation is the root of all evil. Yet we should not pass up our opportunities in that critical 3%.”

D.E. Knuth

You have to find that 3 % !


Finding the 3 %


Measure

ALWAYS measure effects Measure more than once

• different data gives different results

Sometimes the “improvements” you make won’t be worthwhile or will make things worse.• Take those out

You need a performance regression test suite


“Measure twice, cut once”carpenter’s adage


Measuring performance

4GL profiler a watch the time, timex commands instrument your code log files


The 4GL profiler

See $DLC/src/samples/profiler/readme.doc Get the “profiler control tool” from PSDN No code changes needed Tells you:

• Time spent in various parts of your program• Call hiearchy• Number of times each part is executed

Learn how to use it! Profile your application


Measuring with etime()

def var startTime as int64 no-undo.def var endTime as int64 no-undo.

startTime = etime(false). for each customer: end.endTime = etime(false).

display endTime - startTime.


Measuring with datetime

def var startTime as datetime no-undo.def var endTime as datetime no-undo.def var elapsedTime as int64 no-undo.

startTime = now. for each customer: end.endTime = now.

elapsedTime = interval (endTime, startTime, "milliseconds").display elapsedTime.


How to optimise


How to optimise

Start with working code and tests You DON’T know where the problem is The problem will move Try one thing at a time Remove changes that didn’t work Know when to stop


How to optimise:various tips and techniquesin no particular order


Comments and white space do notimpede performance.

What is the most important thing?


Which algorithm is faster?

def var n as integer no-undo.def var sum as integer no-undo.

sum = 0. do n = 1 to 1000: sum = sum + n. end.

n = 1000. sum = (n * (n + 1)) / 2.


Avoid Unnecessary XML

Parsing XML uses many cpu cycles XML is a memory hog XML documents are often big


Clean your room

Delete dynamic objects and widgets you don’t need anymore• dynamic object tracker

• session:system:first-procedure, etc

Use widget pools Get rid of temp tables you don’t need Get rid of objects you don’t need


Temp tables

Pass BY-REFERENCE or pass handle Raise -Bt

• -Bt sets number of temp-table buffers• default is low

Use EMPTY TEMP-TABLE when possible, instead of FOR EACH tt: DELETE tt. END.

Use MIN-SCHEMA-MARSHAL or NO-SCHEMA-MARSHAL attribute when passing TTs to/from app servers


Use NO-UNDO Variables

def var foo as integer no-undo.def var bar as character no-undo.

(would have been nice if this hadbeen the default behaviour,but is not)


Group assigns

assign i = 3 j = 5 c = “abcdef” .

i = 3. j = 5. c = “abcdef”.

NoYes


BUFFER-COPY beats ASSIGN

BUFFER-COPY source TO target

optionsEXCEPT list

USING list

NO-LOBS


Avoid redundant code

Do calculations once and reuse result wherever possible

j = someFunction ().do i = 1 to 10: stuffend. do i = 1 to 10:

stuff j = someFunction ().end.


Redundant code

do n = 1 to someFunctionOrOther(): … stuff.end.

i = someFunctionOrOther(). do n = 1 to i: … stuff. end.


Eliminate unnecessary code

Code that isn’t there executes in zero time

“If we wish to count lines of code, we should not regard them as lines produced but as lines spent.”

Edsger Dijkstra

“Inside every large program there is a small program trying to get out.”

Sir Tony Hoare


Loop hoisting

do I = 1 to 50: if expression1 then run bar(). else do: if expression2 then do: run foobar(). end. else run foo(). end.end.

if expression1 then do I = 1 to 50: run bar(). end.else do: if expression2 then do I = 1 to 50: run foobar(). end. else do I = 1 to 50: run foo(). end.end.


DO instead of REPEAT

sum = 0. repeat n = 1 to 10000: sum = sum + n. end.

sum = 0. do n = 1 to 10000: sum = sum + n. end.

63 milliseconds 57 milliseconds


Minimise block nesting

IF expression THEN statement.

instead of

IF expression THEN DO: statement. END.


Use CASE instead of nested IF

CASE status: WHEN 1 THEN DO: END.

WHEN 2 THEN DO: END.

WHEN 3 THEN DO: END.

OTHERWISE DO: END.END.


Increase sort buffers

Set -TB to 31 (buffer size) Set -TM to 24 (number of merge buffers)


Avoid deep object hierarchies

constructors have to be run for each class you inherit from

destructors have to be run for each class you inherit from

CLASS A:END CLASS.

CLASS B INHERITS A:END CLASS.

CLASS C INHERITS B:END CLASS.

CLASS D INHERITS C:END CLASS.

new (D) runs 4 constructors


Minimise creation of subprocesses

Creating a process is one of the most expensive system calls


Duff’s Device

switch (count % 8) { case 0: do { *to = *from++; case 7: *to = *from++; case 6: *to = *from++; case 5: *to = *from++; case 4: *to = *from++; case 3: *to = *from++; case 2: *to = *from++; case 1: *to = *from++; } while ((count -= 8) > 0); }


Use sequences

Does not require locking records Can cause gaps in numbering though You can use UUID’s for unique keys instead

of sequences

10.1B has 64-bit sequences


Queries

Avoid unindexed CAN-FIND Use word indexes for status indicators Avoid queries on boolean values Careful with OR predicates in WHERE

clauses Add more indexes Get rid of unused indexes COMPILE XREF Exchange sessions on indexing


HIDE screen data while calculating

See recent PEG thread on LockWindowUpdate• search for “window update” to find it.


Avoid CONNECT

CONNECT is somewhat slow

CONNECT at runtime requires r/w access to database files (insecure)


Propath

use -q option• propath search is done only once

Keep propath as short as possible• The more entries in propath the longer the

searches can take

Order entries by frequency of use• Put most frequently used in front


Shared Procedure libraries

Use when same code run by multiple sessions ON SAME MACHINE

Whole library is mapped in one call Saves memory due to single copy

• Memory can then be used to improve performance

– Bigger database buffer pool– More users– Can reduce paging (if you are)

Marginally faster due to opening fewer .r files


Cost of RUN

type relative time (ymmv)

internal procedure 1 ( ~ 5 microseconds)

persistent procedure 1.5

external procedure 2.3

web service invocation ~ 1,000 to 15,000

web service invocation time is highly variable and depends on:processor speednetwork speednumber of hopsdistancetime of dayday of weekload on serverwhich wsdl and soap options are used


More stuff

Compile with -min-size option Use shared memory database connections

when possible (avoid networking) Single user mode usually isn’t fastest

• compared to multi-user with 1 user


Measure

Sometimes the changes you make won’t be worthwhile

ALWAYS measure effects Measure more than once

• with different data

Batch jobs should always write to a log file• Watch for changes in duration over time


Code Reviews

You don’t know everything You might have overlooked something There might be a better way


Other things to do


Other things to do

Add more memory Simplify your application Tune your database

• See “OpenEdge® RDBMS Performance Tuning Made Simple” on PSDN or PEG

DataServers• “Building High Performance Applications with the

Progress Oracle DataServer” on PSDN

• “DataServer Best Practices” on PSDN


Where to learn more

The PEG (www.peg.com) PSDN (psdn.progress.com) 4GL Programming Handbook Past Exchange sessions Progress course on ABL performance


Questions

dev-21: optimising your abl for performance making your code go faster gus björklund wizard,...

Documents

performance measure

performance things

problem slide

causes slide

wulf slide

machine better performance

carpenters adage slide

faster disks