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From Remko Popma <rem...@yahoo.com>
Subject Re: async logger on slow single core env performs 50% worse than log4j v1
Date Sat, 27 Jul 2013 09:39:52 GMT
I quickly reviewed the code and as far as I can tell:
* only the following places in Log4j-2 will create a permanent thread in addition to your
application threads: AsyncLoggers, AsyncAppenders, o.a.l.l.c.net.SocketServer, o.a.l.l.c.net.UDPSocketServer
and o.a.l.l.c.helpers.*CachedClock
* synchronous logging will not create any threads
* RollingFile creates a short-lived thread for the roll-over, *only* if the old file needs
to be compressed to a .zip or .gz file (the file rename action is synchronous)

So I'm thinking that the difference in CPU usage is caused by something other than threads
or async logging.
I'd be interested in your answers to my questions below.

Best regards,
Remko


________________________________
 From: Remko Popma <remkop@yahoo.com>
To: Log4J Users List <log4j-user@logging.apache.org> 
Sent: Saturday, July 27, 2013 12:53 PM
Subject: Re: async logger on slow single core env performs 50% worse than log4j v1
 

I don't think we've ever done any performance testing on the kind of environment you describe,
so this is great feedback, thanks!

First, configuration via XML instead of sys props is on the todo list.

Second, you mentioned you use system property "AsyncLoggerContextSelector" to switch on AsyncLoggers.
This is incorrect. The correct key is "Log4jContextSelector" (and that would explain why removing
this setting made no difference).

Third, if I understand correctly you are essentially logging to a memory-mapped file. In that
case any buffering is just wasting CPU resources, so you should not use the Fast*File appenders
as their buffering cannot be switched off. (Non-Fast) FileAppenders also use bufferedIO=true
by default, but you can switch this off in config. I would expect this to save some CPU.

On that note, you mentioned CPU usage as your performance measure. Is that the most important
number? Do you have any throughput/latency goals?
Do you have any tools on your platform to see what the CPU is doing? Which threads are busy
for example?

In terms of GC, making all loggers Async has a small benefit in that it re-uses log event
objects.


I am still intrigued by the difference in CPU usage you mention between log4j-1.2 and 2.0.
Is your application code exactly the same? Or do you use the pattern formats that are now
available in log4j-2.0?

Regards,
Remko


________________________________
From: "SMITH, CURTIS" <cs0428@att.com>
To: Log4J Users List <log4j-user@logging.apache.org> 
Sent: Saturday, July 27, 2013 6:55 AM
Subject: RE: async logger on slow single core env performs 50% worse than log4j v1


LOL well that's obvious now.  :)  It was more a case of wishful thinking and why not give
it a "try".    But it's still odd that my attempts to slim it down It's still 2x worse than
v1.  Something else is in play.

curt

-----Original Message-----
From: Ralph Goers [mailto:ralph.goers@dslextreme.com] 
Sent: Friday, July 26, 2013 5:34 PM
To: Log4J Users List
Subject: Re: async logger on slow single core env performs 50% worse than log4j v1

I'm curious why you are even trying to use Async anything with a single core environment (unless
it is hyper-threaded). Only 1 thread can be active at a time so when you switch threads the
active thread will just stop. This won't gain you any additional throughput but you will still
incur the additional overhead of thread management and locking.

Ralph

On Jul 26, 2013, at 1:55 PM, SMITH, CURTIS wrote:

> I removed  System.setProperty("AsyncLoggerContextSelector", "org.apache.logging.log4j.core.async.AsyncLoggerContextSelector");
> No change in CPU, but going from FastRollingFile to RollingFile I got back 10% of my
lost CPU.  Still at 40% CPU where v1 runs at 20%.
> 
> I would like to get down to the equivalent behavior as we got from log4j v1, then try
v2 features to get it better.  Since I'm still seeing worse performance, I'm guessing that
there's still one or more threads under the hood vs V1 with:  sync Logger and RollingFile.
> 
> Any guesses for me to try?
> 
> Tnx curt
> 
> _____________________________________________
> From: SMITH, CURTIS
> Sent: Friday, July 26, 2013 1:16 PM
> To: log4j-user@logging.apache.org
> Subject: async logger on slow single core env performs 50% worse than log4j v1
> 
> 
> I suspect a slow single core env is a new scenario for v2 and async logger.   My view
is that there's a mis match between v2's async logger thread design that works great on multi-core
envs and this embedded slow single core env...   Sooo I need to try a few different configurations
to see what does run best on a slow single core...
> 
> But I need your tips as to what I might change / tune to get v2 to perform as good or
better than v1 in a single core env.
> 
> FWIW:  log4j v1 ran my standard use case test averaging 20% CPU.  Log4j v2 ran at 50%
CPU, so more than 2x worse.
> 
> Our business logic is highly threaded so any subsystem that has a "hot" thread like this
config that has 5 loggers and 3 appenders I might be shooting myself in the foot.  You know
this new design the best so I'm open as to what to pick and choose from v2 that is likely
to perform the best?
> 
> FYI:  I feel using system properties vs exclusively using declarative configuration
all within the log4j2.xml separates out configuration.  I'd prefer to not have to use system
properties for any configuration.
> 
> My first experiment will be to remove the async logger property.
> 
> Any thoughts re the FastRollingFile appender or any other tuning that might be better
for a single core env.  It's a slow Arm v5 or so, pretty old and lacking the better context
switching features of newer chips.  The VM is also slow,  IBM J9 J2ME JDK1.6.   Benchmarking
the J9 vs Oracle J2ME, J9 is real slow and poor at thread context switching.  But you get
what you pay for, J9 is also real cheap.
> 
> ******
> ******
> Note:  the log files are on /tmp a memory FS in our env.  So the worst case of a synchronous
logger from the same thread as the logger.debug call may not perform that badly thanks to
Linux FS buffering and memfs having low latency.  Just mentioning.
> 
> 
> // Manually set the log4j v2 async logger tuning parameters here.  DLA does not have
a system property
>                // property file
>                System.setProperty("AsyncLoggerContextSelector", "org.apache.logging.log4j.core.async.AsyncLoggerContextSelector");
>                System.setProperty("AsyncLogger.RingBufferSize", "128");   
    // min size permissable to keep memory low
>                System.setProperty("AsyncLogger.WaitStrategy", "Block");   
    // less CPU, better for embedded env
>                System.setProperty("log4j2.disable.jmx", "true");         
             // saves on a jmx jar and we don't use JMX anyway
> 
> <?xml version="1.0" encoding="UTF-8"?>
> <configuration status="trace" level="trace" >  <!-- log4j v2 debug add these:
status="trace" level="trace" -->
>        <appenders>
>                <FastRollingFile name="DLA"
>                        fileName="/tmp/att/sync/log/dla.log"
>                        filePattern="/tmp/att/sync/log/dla.log.%i" append="true">
>                        <PatternLayout>
>                                <pattern>[%d][%-5p][%-15t][%-15c{1}]:%m%n</pattern>
>                        </PatternLayout>
>                        <Policies>
>                                <SizeBasedTriggeringPolicy size="3
MB" />
>                        </Policies>
>                        <DefaultRolloverStrategy max="2" />
>                </FastRollingFile>
>                <FastRollingFile name="DEVICES"
>                        fileName="/tmp/att/sync/log/dla_devices.log"
>                        filePattern="/tmp/att/sync/log/dla_devices.log.%i"
append="true">
>                        <PatternLayout>
>                                <pattern>[%d][%-5p][%-15t][%-15c{1}]:%m%n</pattern>
>                        </PatternLayout>
>                        <Policies>
>                                <SizeBasedTriggeringPolicy size="3
MB" />
>                        </Policies>
>                        <DefaultRolloverStrategy max="1" />
>                </FastRollingFile>
>                <FastRollingFile name="VIDEO"
>                        fileName="/tmp/att/sync/log/dla_video.log"
>                        filePattern="/tmp/att/sync/log/dla_video.log.%i" append="true">
>                        <PatternLayout>
>                                <pattern>[%d][%-5p][%-15t][%-15c{1}]:%m%n</pattern>
>                        </PatternLayout>
>                        <Policies>
>                                <SizeBasedTriggeringPolicy size="3
MB" />
>                        </Policies>
>                        <DefaultRolloverStrategy max="1" />
>                </FastRollingFile>
>                <Console name="CO" target="SYSTEM_OUT">
>                        <PatternLayout pattern="%d %-5p [%t] %C{2} (%F:%L)
- %m%n" />
>                </Console>
>        </appenders>
>        <loggers>
>                <logger name="com.att.dlc.afm" additivity="false" >
>                        <appender-ref ref="DLA" />
>                </logger>
>                <logger name="com.att.dlc.devices" additivity="false" level="debug">
>                        <appender-ref ref="DEVICES" />
>                </logger>
>                <logger name="com.att.dlc.util.serialport" additivity="false"
level="debug">
>                        <appender-ref ref="DEVICES" />
>                </logger>
>                <logger name="com.att.dlc.webcamserver" additivity="false"
level="debug">
>                        <appender-ref ref="VIDEO" />
>                </logger>
>                <logger name="com.att.dlc.devices.cameras" additivity="false"
level="debug">
>                        <appender-ref ref="VIDEO" />
>                </logger>
>                <root level="debug">
>                        <appender-ref ref="DLA" />
>                </root>
>        </loggers>
> </configuration>
> 
> Curt Smith
> AT&T Digital Life
> DLC Software Development
> 404-499-7013
> (cell) 678-365-6508
> 
> 
> 


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