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by Roger PenceASNA Education Director

Maximum velocity: How to get the Maximum velocity: How to get the most performance from your AVR most performance from your AVR appsapps

Paying attention to just a few details can make your programs faster and more efficient

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Overview of topicsOverview of topics

• Use connection pooling to improve file IO performance

• Using the singleton DB pattern• Beware shared DB’s• Using threading to improve performance

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The proper use of connection pooling

No single thing will more improve Web application performance that proper use of connection pooling

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What is connection pooling?What is connection pooling?

• Connection pooling is DataGate’s ability to “reuse” database server jobs between stateless IO requests

• Connection pooling applies mostly to stateless Web applications or Web services.

• Rarely is connection pooling helpful to Windows-based programs– It’s not likely to hurt anything, but connection

pooling is especially suited for stateless apps

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Connection pooling: the System iConnection pooling: the System i

• Effective connection pooling is especially important if the System i is your database platform

• Without connection pooling, a new OS/400 job must be created for each request. This can take 3-10 seconds—depending on System i load and configuration

• With connection pooling, an OS/400 job is made available to a request in a matter of milliseconds

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Connection pooling: SQL ServerConnection pooling: SQL Server

• Although instancing a database connection isn’t quite the performance drain on SQL Server that it is on the System i, it’s still a drain

• It may also positively effect SQL Server licensing– Because you are in effect also pooling licensing (for

CAL-based licenses)– Connection pooling keeps any one connection is play

for the minimum amount of time• This discussion is primarily System i-centric, but

everything said here about connection pooling also applies to DataGate for SQL Server

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Enabling connection poolingEnabling connection pooling

• Connection pooling can be enabled statically through database name attributes

• Or set dynamically through changing the database object’s PoolingTimeOut property prior to connecting that object

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Enabling connection pooling staticallyEnabling connection pooling statically

• Connection pooling is enabled with the DataGate Database Manager’s “Work with Database Names”panel

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Enabling connection pooling Enabling connection pooling dynamicallydynamically

• Connection pooling can also be controlled by setting the database object’s PoolingTimeout value.

• Any value greater than zero sets the connection pooling timeout value (in minutes); zero disables connection pooling

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What’s a good time-out value?What’s a good time-out value?

• That depends. • For many shops, something in the range of 20

minutes or so works well• However, we have customers that use much

larger values if the latency between pages is extreme– Shop floor browser-based applications for example

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How does connection pooling it work?How does connection pooling it work?

• Red zone= inactive pooled jobs• Green zone = active jobs• At this point, application has no jobs pooled

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Blue and pink: cool and warmBlue and pink: cool and warm

• For purposes of this discussion:– Blue users get new, previously unpooled jobs.

These uses wait 3-7 seconds for their page.– Blue jobs are new, previously unpooled jobs.– Pink users get a pooled job. These users wait just a

few milliseconds for their page.– Pink jobs are previously pooled jobs.

Think of it this way, blue users/jobs are cool; pink users/jobs are warm!

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A user request occursA user request occurs

• DataGate first looks in the red job zone for a previously pooled job. There isn’t one. DataGate starts a new one.

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The job is now pooledThe job is now pooled

• When the server is done servicing the user’s request, the job is “moved” to the pooled zone

• Pooled jobs have no open files, no activity, and consume very few OS/400 resources

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Same user requests a second pageSame user requests a second page

• Because there is a job in the pooled zone, that job is made available in just a few milliseconds

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The job is put back in the poolThe job is put back in the pool

• When the server is done servicing the user’s request, the job is “moved” to the pooled zone again

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Two users request a page within 1 MS Two users request a page within 1 MS of each otherof each other• The first user gets the previously pooled job• The second user has to wait for OS/400 to create a

new job

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Now two jobs are pooledNow two jobs are pooled

• Two jobs are pooled• With two jobs pooled, the two users are both

guaranteed a pooled job

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Three users request a page within a Three users request a page within a couple of MS of each othercouple of MS of each other• Two user get a pooled job; the third user waits for a new job • For most Web apps, jobs aren’t unique to a user, so the two

pooled jobs are avaiable to the first two users—independent of who previously used the two pooled jobs

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Now three jobs are pooledNow three jobs are pooled

• The inactive job pool is now somewhat populated• Lots of users can come and go through these

three jobs

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The benefit of a populated pooled The benefit of a populated pooled zonezone• As the pooled zone gets populated, it less

likely that new jobs will be needed• After get five or six pooled, what are the

chances that five or six users will each request a page within a few hundred or so milliseconds of each other?

• Of course, it could happen. And if it does, a new job is added and the pooled zone grows by one

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20 or 30 to one!20 or 30 to one!

• ASNA benchmarks show that you can expect at least 20 or 30 users able to do “normal” work using a single pooled job

• As the load grows, so grows the pooled zone• But pooled jobs have a very low impact on the

System i

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Lots of users busy with few jobs

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How does the pooled zone get cleared How does the pooled zone get cleared outout• By job timeout value– First in, first out

• For example with no activity, a job drops out of the pooled zone when its timeout value expires

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How to tell if it’s workingHow to tell if it’s working

• Performance is a very good way to tell if connection pooling is working

• However, another wau to ensure it’s working is to test you’re app, through several pages, knowing only one user is using it

• If, after using the app for a while you have more than one OS/400 job active, something is amiss

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Something is wrong here!There are three jobs for a application with a single user!

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Something else to watch forSomething else to watch for

• It’s possible to be using connection pooling correctly and still get more than one job active

• This can happen when a Web page uses one or more secondary classes where each of which establishes its own DB connection

• This topic is out of the scope of this presentation, but if you think this is happening to you, ask me offline for a copy of the Singleton DB pattern explanation

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The rules of connection poolingThe rules of connection pooling

• Enable it either statically or dynamically• The next point is very important!• Each page must following this cycle:– Connect the DB– Open files– Do work– Close files– Disconnect the DB

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Your app must disconnect for every Your app must disconnect for every page!page!

• A job gets moved back to the pooled zone when it’s disconnect

• If you don’t disconnect, you aren’t pooling jobs!

• The Page’s Unload event is a good place to put your closes and disconnect

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Consider doing this:Consider doing this:

• Use Close *All to close all files– This gracefully closes all open files– Doesn’t choke if none are opened

• Then disconnect

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Don’t forget to close files!Don’t forget to close files!

• If you disconnect but don’t close files, you cause lots of filesto be opened!

• Close *All• then disconnect

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Remember this!Remember this!

• If you don’t close files and disconnect the DB object before the page goes out of scope, you are not using connection pooling!

• The same advice applies to Web methods. Close files and disconnect the DB after every Web method call

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Your app must disconnect for every Your app must disconnect for every page!page!

• A job gets moved back to the pooled zone when it’s disconnected

• If you don’t disconnect, it’s an orphan active job

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Pooled connection scopePooled connection scope

• Pooled connections are uniquely identified by all of the properties of a database name.

• Thus, if each user is signing on to your Web app with her user profile and password, you are negating the scalable benefits of connection pooling– You are however, letting users get their jobs back

quickly

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Pooled connection scopePooled connection scope

• Some shops can’t use a single database name for all users (ie, a single user ID and password). Thanks SOX.

• Consider using three or database names to group users (perhaps by security or function)

• This way you’re at least getting some scalability by letting each group share pooled jobs

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Limiting database platform jobsLimiting database platform jobs

• When you instance a class that has a DB object, and that class connects, that class gets its own job on the database platform

• This means that it’s very easy for any one program (Windows or Web) to have several jobs in play for that one program

• This… is not good!

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Limiting database platform jobsLimiting database platform jobs

• Note the following discussion applies to Windows and Web AVR apps, but not to Monarch-generated apps

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An example with two classesAn example with two classes

• Two classes, two DBs, two connects = two jobs

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This is especially troubling on the System i. Scalability goes out the window if you aren’t careful!

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The solution: the singleton DB patternThe solution: the singleton DB pattern

• A parent class passes its job to its children, the children to their children

• Results in just one job for the instance of the program

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The bad scenarioThe bad scenario

• Here both classes get their job

• This effects Windows and Web programs

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To limit the database platform one job, the parent class needs to pass its DB object around to its children (and them to their children if they have any.

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There are just a few rulesThere are just a few rules

• The parent, top level class, must pass its DB object on

• The parent must disconnect the DB• Child can never disconnect– Others might want the job

• Children can connection the DB, but should check to see if it needs to be – Others might have previously connected it

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The singleton DB pattern is well-The singleton DB pattern is well-documenteddocumented

• The downloads for Palooza (associated with this session) includes a detailed description of the singleton DB pattern

• Factor it into all of your programs! • If you don’t, you are risking scalability on your

database server

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Beware shared DB connections!Beware shared DB connections!

• Do not share DB connections in Web applications

• This forces all users to wait on a single thread for DB connections

• This is guaranteed to make you stay up late at night

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Consider (carefully) if using threading Consider (carefully) if using threading can help your application performancecan help your application performance

• Spinning off certain processes can help application performance

• One place where using threading is effective is to cause Web services to fire off a thread (to start a long-running process) and quickly return

• Here is an abbreviated example…

Spinning off the SubmitPrint process on its own thread.

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In summaryIn summary

• Use connection pooling. Properly!• Dispatch the KeyList where it makes sense• Use SetRange/ReadRange instead of

SETLL/READE• Populate lists from read-only files• Don’t persist record locks longer than

necessary

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