In log4j does checking isDebugEnabled before logging improve performance

Question

I am using Log4J in my application for logging  Previously I was using debug call like   Option 1   logger debug  some debug text      but some links suggest that it is better to check isDebugEnabled   first  like    Option 2   boolean debugEnabled   logger isDebugEnabled    if  debugEnabled        logger debug  some debug text        So my question is  Does option 2 improve performance any way     Because in any case Log4J framework have same check for debugEnabled  For option 2 it might be beneficial if we are using multiple debug statement in single method or class  where the framework does not need to call isDebugEnabled   method multiple times  on each call   in this case it calls isDebugEnabled   method only once  and if Log4J is configured to debug level then actually it calls isDebugEnabled   method twice    In case of assigning value to debugEnabled variable  and Actually called by logger debug   method    I don t think that if we write multiple logger debug   statement in method or class and calling debug   method according to option 1 then it is overhead for Log4J framework in comparison with option 2  Since isDebugEnabled   is a very small method  in terms of code   it might be good candidate for inlining

User · Answer

Since many people are probably viewing this answer when searching for log4j2 and nearly all current answers do not consider log4j2 or recent changes in it, this should hopefully answer the question.

log4j2 supports Suppliers (currently their own implementation, but according to the documentation it is planned to use Java's Supplier interface in version 3.0). You can read a little bit more about this in the manual. This allows you to put expensive log message creation into a supplier which only creates the message if it is going to be logged:

LogManager.getLogger().debug(() -> createExpensiveLogMessage());

User · Answer

In Java 8  you don t have to use isDebugEnabled   to improve the performance   https   logging apache org log4j 2 0 manual api html Java 8 lambda support for lazy logging  import java util logging Logger      Logger getLogger  hello   info    - gt   Hello     name

User · Answer

Since Log4j version 2 4  orslf4j-api 2 0 0-alpha1  it s much better to use fluent API  or Java 8 lambda support for lazy logging   supporting Supplier lt   gt  for log message argument  that can be given by lambda   log debug  Debug message with expensive data                       - gt  doExpensiveCalculation       OR with slf4j API   log atDebug                addArgument    - gt  doExpensiveCalculation                 log  Debug message with expensive data

User · Answer

It improves the speed because it s common to concatenate strings in the debug text which is expensive eg   boolean debugEnabled   logger isDebugEnabled    if  debugEnabled        logger debug  some debug text    someState

User · Answer

Option 2 is better   Per se it does not improve performance  But it ensures performance does not degrade  Here s how   Normally we expect logger debug someString    But usually  as the application grows  changes many hands  esp novice developers  you could see  logger debug str1   str2   str3   str4    and the like   Even if log level is set to ERROR or FATAL  the concatenation of strings do happen   If the application contains lots of DEBUG level messages with string concatenations  then it certainly takes a performance hit especially with jdk 1 4 or below   Iam not sure if later versions of jdk internall do any stringbuffer append      Thats why Option 2 is safe  Even the string concatenations dont happen

User · Answer

In this particular case  Option 1 is better   The guard statement  checking isDebugEnabled    is there to prevent potentially expensive computation of the log message when it involves invocation of the toString   methods of various objects and concatenating the results   In the given example  the log message is a constant string  so letting the logger discard it is just as efficient as checking whether the logger is enabled  and it lowers the complexity of the code because there are fewer branches   Better yet is to use a more up-to-date logging framework where the log statements take a format specification and a list of arguments to be substituted by the logger mdash but  lazily   only if the logger is enabled  This is the approach taken by slf4j   See my answer to a related question for more information  and an example of doing something like this with log4j

User · Answer

As of 2 x  Apache Log4j has this check built in  so having isDebugEnabled   isn t necessary anymore  Just do a debug   and the messages will be suppressed if not enabled

User · Answer

Since in option 1 the message string is a constant  there is absolutely no gain in wrapping the logging statement with a condition  on the contrary  if the log statement is debug enabled  you will be evaluating twice  once in the isDebugEnabled   method and once in debug   method  The cost of invoking isDebugEnabled   is in the order of 5 to 30 nanoseconds which should be negligible for most practical purposes  Thus  option 2 is not desirable because it pollutes your code and provides no other gain

User · Answer

I would recommend using Option 2 as de facto for most as it s not super expensive     Case 1   log debug  one string     Case2   log debug  one string     two string    object toString   object2 toString    At the time either of these are called  the parameter string within log debug  be it CASE 1 or Case2  HAS to be evaluated    That s what everyone means by  expensive    If you have a condition before it   isDebugEnabled     these don t have to be evaluated which is where the performance is saved

User · Answer

For a single line  I use a ternary inside of logging message  In this way I don t do the concatenation   ej   logger debug str1   str2   str3   str4     I do   logger debug logger isDebugEnable   str1   str2   str3   str4 null     But for multiple lines of code  ej   for Message mess list        logger debug  mess     mess getText         I do    if logger isDebugEnable          for Message mess list             logger debug  mess     mess getText

User · Answer

Like  erickson it depends  If I recall  isDebugEnabled is already build in the debug   method of Log4j  As long as you re not doing some expensive computations in your debug statements  like loop on objects  perform computations and concatenate strings  you re fine in my opinion   StringBuilder buffer   new StringBuilder    for Object o   myHugeCollection     buffer append o getName    append         buffer append o getResultFromExpensiveComputation    append         log debug buffer toString       would be better as   if  log isDebugEnabled      StringBuilder buffer   new StringBuilder      for Object o   myHugeCollection       buffer append o getName    append           buffer append o getResultFromExpensiveComputation    append             log debug buffer toString

User · Answer

Log4j2 lets you format parameters into a message template  similar to String format    thus doing away with the need to do isDebugEnabled     Logger log   LogManager getFormatterLogger getClass     log debug  Some message  myField  s    myField     Sample simple log4j2 properties   filter threshold type   ThresholdFilter filter threshold level   debug appender console type   Console appender console name   STDOUT appender console layout type   PatternLayout appender console layout pattern    d  -5p   c -  m n appender console filter threshold type   ThresholdFilter appender console filter threshold level   debug rootLogger level   info rootLogger appenderRef stdout ref   STDOUT

User · Answer

As others have mentioned using the guard statement is only really useful if creating the string is a time consuming call  Specific examples of this are when creating the string will trigger some lazy loading   It is worth noting that this problem can be completed avoided by using Simple Logging Facade for Java or  SLF4J  - http   www slf4j org manual html   This allows method calls such as   logger debug  Temperature set to     Old temperature was       t  oldT     This will only convert the passed in parameters to strings if debug is enabled  SLF4J as its name suggests is only a facade and the logging calls can be passed to log4j   You could also very easily  roll your own  version of this   Hope this helps

User · Answer

If you use option 2 you are doing a Boolean check which is fast  In option one you are doing a method call  pushing stuff on the stack  and then doing a Boolean check which is still fast  The problem I see is consistency  If some of your debug and info statements are wrapped and some are not it is not a consistent code style  Plus someone later on could change the debug statement to include concatenate strings  which is still pretty fast  I found that when we wrapped out debug and info statement in a large application and profiled it we saved a couple of percentage points in performance  Not much  but enough to make it worth the work  I now have a couple of macros setup in IntelliJ to automatically generate wrapped debug and info statements for me

User · Answer

Using the isDebugEnabled   is reserved for when you re building up log messages by concatenating Strings   Var myVar   new MyVar    log debug  My var is     myVar      value     myVar someCall       However  in your example there is no speed gain as you re just logging a String and not performing operations such as concatenation  Therefore you re just adding bloat to your code and making it harder to read   I personally use the Java 1 5 format calls in the String class like this   Var myVar   new MyVar    log debug String format  My var is   s   value    s    myVar  myVar someCall        I doubt there s much optimisation but it s easier to read   Do note though that most logging APIs offer formatting like this out of the box  slf4j for example provides the following   logger debug  My var is      myVar     which is even easier to read

User · Answer

Short Version  You might as well do the boolean isDebugEnabled   check   Reasons  1- If complicated logic   string concat  is added to your debug statement you will already have the check in place  2- You don t have to selectively include the statement on  complex  debug statements   All statements are included that way  3- Calling log debug executes the following before logging     if repository isDisabled Level DEBUG INT             return    This is basically the same as calling log  or cat  isDebugEnabled      HOWEVER   This is what the log4j developers think  as it is in their javadoc and you should probably go by it     This is the method   public   boolean isDebugEnabled          if repository isDisabled  Level DEBUG INT         return false      return Level DEBUG isGreaterOrEqual this getEffectiveLevel           This is the javadoc for it          Check whether this category is enabled for the  lt code gt DEBUG lt  code gt     Level        lt p gt  This function is intended to lessen the computational cost of    disabled log debug statements        lt p gt  For some  lt code gt cat lt  code gt  Category object  when you write      lt pre gt         cat debug  This is entry number      i        lt  pre gt        lt p gt You incur the cost constructing the message  concatenatiion in    this case  regardless of whether the message is logged or not        lt p gt If you are worried about speed  then you should write     lt pre gt       if cat isDebugEnabled             cat debug  This is entry number      i               lt  pre gt        lt p gt This way you will not incur the cost of parameter    construction if debugging is disabled for  lt code gt cat lt  code gt   On    the other hand  if the  lt code gt cat lt  code gt  is debug enabled  you    will incur the cost of evaluating whether the category is debug    enabled twice  Once in  lt code gt isDebugEnabled lt  code gt  and once in    the  lt code gt debug lt  code gt    This is an insignificant overhead    since evaluating a category takes about 1   of the time it    takes to actually log        return boolean -  lt code gt true lt  code gt  if this category is debug    enabled   lt code gt false lt  code gt  otherwise

[java] In log4j, does checking isDebugEnabled before logging improve performance?

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