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https://issues.apache.org/jira/browse/LOG4J2-1349?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15432877#comment-15432877
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Remko Popma edited comment on LOG4J2-1349 at 8/23/16 3:10 PM:
--------------------------------------------------------------
h1. Corrected & Additional Benchmarks
!v2_ThreadContextPut.png!
How long it takes to add a single key-value pair in a ThreadContext that
already contains 5, 50 or 500 elements.
!v2_ThreadContextGet.png!
How long it takes to get a single key-value pair from a ThreadContext that
contains 5, 50 or 500 elements.
!v2_InjectWithoutConfigProperties.png!
Injecting is the operation of copying data from the thread context to a log
event. "Inject without config properties" is the happy case where there are no
List<Property> key-value pairs from the configuration. For a copy-on-write
thread context we can use the current thread context snapshot without any
further modifications. This is very fast.
"Legacy" means the Log4jLogEvent::createMap implementation that is in current
master (copy from the ThreadContext's Map<String,String> to the LogEvent's
Map<String,String> context map).
"Default" means the ThreadContext uses a Map<String, String> but the LogEvent
has a ContextData field.
"CopyOpenHash" and "CopySortedArray" are copy-on-write ThreadContextMap
implementations.
"NoGcOpenHash" and "NoGcSortedArray" are ThreadContextMap implementations that
avoid creating temporary objects.
!v2_InjectWithConfigProperties.png!
The other inject case is where we need to copy data from _both_ the thread
context _and_ the configuration's List<Property> key-value pairs. Here we
cannot just use the reference; we need to do some additional copying even if
the thread context is copy-on-write.
Here also, "Legacy" means the Log4jLogEvent::createMap implementation that is
in current master (copy from the ThreadContext's Map<String,String> to the
LogEvent's Map<String,String> context map), and "Default" means the
ThreadContext uses a Map<String, String> but the LogEvent has a ContextData
field.
"CopyOpenHash" and "CopySortedArray" are copy-on-write ThreadContextMap
implementations. "NoGcOpenHash" and "NoGcSortedArray" are ThreadContextMap
implementations that avoid creating temporary objects.
!v2_DataStructOpsPerfSmallDataSet.png!
Fixed benchmark to measure a single put and a single get operation against a
data structure containing 5 items.
!v2_DataStructOpsPerfMediumDataSet.png!
Fixed benchmark to measure a single put and a single get operation against a
data structure containing 500 items.
The performance of the "get" operation is important, but a common use case is
also to iterate over _all_ elements in the LogEvent's context data, so
iteration performance is also noteworthy.
h3. Conclusion
If we agree to use ContextData in LogEvents (LOG4J2-1447, to allow non-String
values in the context data), then having a ThreadContextMap based on the same
data structure gives significantly better performance when putting values into
the ThreadContext and when copying data into the LogEvent.
When it comes to using a copy-on-write ThreadContextMap or a garbage-free
implementation, the first consideration is whether the configuration declares
<Property> values or not, the second consideration is how often the application
puts new key-value pairs in the ThreadContext. We can make copy-on-write the
default and provide an option for applications to configure a garbage-free
ThreadContextMap.
Finally, ArrayContextData vs OpenHashContextData: the hash-based data structure
give slightly better {{get}} performance, but the array-based structure gives
_much_ better {{inject}} performance when the configuration declares <Property>
values, so overall I think ArrayContextData is the better choice.
was (Author: [email protected]):
h1. Corrected & Additional Benchmarks
!v2_ThreadContextPut.png!
How long it takes to add a single key-value pair in a ThreadContext that
already contains 5, 50 or 500 elements.
!v2_ThreadContextGet.png!
How long it takes to get a single key-value pair from a ThreadContext that
contains 5, 50 or 500 elements.
!v2_InjectWithoutConfigProperties.png!
Injecting is the operation of copying data from the thread context to a log
event. "Inject without config properties" is the happy case where there are no
List<Property> key-value pairs from the configuration. For a copy-on-write
thread context we can use the current thread context snapshot without any
further modifications. This is very fast.
"Legacy" means the Log4jLogEvent::createMap implementation that is in current
master (copy from the ThreadContext's Map<String,String> to the LogEvent's
Map<String,String> context map).
"Default" means the ThreadContext uses a Map<String, String> but the LogEvent
has a ContextData field.
"CopyOpenHash" and "CopySortedArray" are copy-on-write ThreadContextMap
implementations.
"NoGcOpenHash" and "NoGcSortedArray" are ThreadContextMap implementations that
avoid creating temporary objects.
!v2_InjectWithConfigProperties.png!
The other inject case is where we need to copy data from _both_ the thread
context _and_ the configuration's List<Property> key-value pairs. Here we
cannot just use the reference; we need to do some additional copying even if
the thread context is copy-on-write.
Here also, "Legacy" means the Log4jLogEvent::createMap implementation that is
in current master (copy from the ThreadContext's Map<String,String> to the
LogEvent's Map<String,String> context map), and "Default" means the
ThreadContext uses a Map<String, String> but the LogEvent has a ContextData
field.
"CopyOpenHash" and "CopySortedArray" are copy-on-write ThreadContextMap
implementations. "NoGcOpenHash" and "NoGcSortedArray" are ThreadContextMap
implementations that avoid creating temporary objects.
!v2_DataStructOpsPerfSmallDataSet.png!
Fixed benchmark to measure a single put and a single get operation against a
data structure containing 5 items.
!v2_DataStructOpsPerfMediumDataSet.png!
Fixed benchmark to measure a single put and a single get operation against a
data structure containing 500 items.
The performance of the "get" operation is important, but a common use case is
also to iterate over _all_ elements in the LogEvent's context data, so
iteration performance is also noteworthy.
h3. Conclusion
If we agree to use ContextData in LogEvents (LOG4J2-1447, to allow non-String
values in the context data), then having a ThreadContextMap based on the same
data structure gives significantly better performance when putting values into
the ThreadContext and when copying data into the LogEvent.
When it comes to using a copy-on-write ThreadContextMap or a garbage-free
implementation, the first consideration is whether the configuration declares
<Property> values or not, the second consideration is how often the application
puts new key-value pairs in the ThreadContext. We can make copy-on-write the
default and provide an option for applications to configure a garbage-free
ThreadContextMap.
Finally, ArrayContextData vs OpenHashContextData: the hash-based data structure
give slightly better {{get}} performance, but the array-based structure gives
_much_ better performance when the configuration declares <Property> values, so
overall I think ArrayContextData is the better choice.
> Garbage-free ThreadContext map
> ------------------------------
>
> Key: LOG4J2-1349
> URL: https://issues.apache.org/jira/browse/LOG4J2-1349
> Project: Log4j 2
> Issue Type: Improvement
> Components: API
> Affects Versions: 2.5
> Reporter: Remko Popma
> Assignee: Remko Popma
> Fix For: 2.7
>
> Attachments: DataStructOpsPerfMediumDataSet.png,
> DataStructOpsPerfSmallDataSet.png, InjectWithConfigProperties.png,
> InjectWithoutConfigProperties.png, ThreadContextPut.png,
> v2_DataStructOpsPerfMediumDataSet.png, v2_DataStructOpsPerfSmallDataSet.png,
> v2_InjectWithConfigProperties.png, v2_InjectWithoutConfigProperties.png,
> v2_ThreadContextGet.png, v2_ThreadContextPut.png
>
>
> The current ThreadContext map and stack implementations allocate temporary
> objects. This ticket is to investigate and track the work for alternative
> implementations that are garbage-free.
> Both DefaultThreadContextMap and DefaultThreadContextStack are copy-on-write
> data structures: each modification replaces the ThreadLocal object with a
> modified copy. The advantage of this approach is that there is no need to
> make a copy for each LogEvent.
> Also, DefaultThreadContextMap uses a JDK map, the JDK collections tend to
> allocate a lot of temporary objects.
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