NLog difference between overflowAction Grow and Block - nlog

Question

I am using NLog in my .Net window service and below are the configuration that i am using for setup Nlog.
<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.nlog-project.org/schemas/NLog.xsd NLog.xsd"
autoReload="true"
throwExceptions="false"
internalLogLevel="Debug" internalLogFile="c:\temp\log.txt">
<targets>
<target xsi:type="AsyncWrapper" name="asyncExceptionDB" overflowAction="Grow" >
<target xsi:type="FallbackGroup" name="String" returnToFirstOnSuccess="true">
<target xsi:type="Database" name="ExceptionDB" dbProvider="System.Data.SqlClient" connectionStringName="nlogconnection" commandType="StoredProcedure" commandText="usp_InsertExceptionLog">
<parameter name="#UserId" layout="${event-properties:item=userId}"/>
<parameter name="#Email" layout="${event-properties:item=email}"/>
<parameter name="#ExceptionType" layout="${event-properties:item=exceptionType}" />
<parameter name="#ExceptionMessage" layout="${event-properties:item=exceptionMessage}" />
<parameter name="#InnerException" layout="${event-properties:item=innerException}" />
<parameter name="#CustomMessage" layout="${message}"/>
<parameter name="#ErrorCode" layout="${event-properties:item=errorCode}" />
</target>
</target>
</target>
<target xsi:type="AsyncWrapper" name="asyncLogDB" overflowAction="Block" >
<target xsi:type="FallbackGroup" name="String" returnToFirstOnSuccess="true">
<target xsi:type="Database" name="LogDB" dbProvider="System.Data.SqlClient" connectionStringName="nlogconnection" commandType="StoredProcedure" commandText="usp_InsertLog">
<parameter name="#UserId" layout="${event-properties:item=userId}"/>
<parameter name="#Email" layout="${event-properties:item=email}"/>
<parameter name="#CustomMessage" layout="${message}"/>
<parameter name="#MeetingId" layout="${event-properties:item=meetingId}" />
<parameter name="#ErrorCode" layout="${event-properties:item=errorCode}" />
</target>
</target>
</target>
<rules>
<!-- add your logging rules here -->
<!-- DO NOT CHANGE NAME HERE (Used in Code) -->
<logger name="SOLog" level="Info" writeTo="asyncLogDB" />
<logger name="SOLog" level="Error" writeTo="asyncExceptionDB" />
<logger name="SOLog" level="Info" writeTo="asyncOHLoggerService" />
<logger name="SOLog" level="Error" writeTo="asyncOHLoggerService" />
<!--<logger name="*" level="Error" writeTo="ExceptionDB" />
<logger name="*" level="Fatal" writeTo="ExceptionDB" />-->
</rules>
</targets>
</nlog>
In my configuration i am using overflow Action value as Grow and Block for different targets. An both work fine in my case as they both write data to there desired destination. But i really didn't understood the difference between both the action Grow and Block. Can any one tell me the actual difference between these two (overflow action Block and Grow) actually the Background details that how they work in background.
I am aware about Grow that it will increase the queue size when it reaches its peak point but one problem of using it in my case with above configuration is that it stop my service and throw an error called OutOfMemoryException and stopped my service after that.
after that i used Block rather then using Grow and my memory utilization is fine in this case and all works fine for me. but the only question that arise in my mind that how come Block is different than Grow. I went through the NLOG documentation but that really didn't help me much to understand the concept of these two i.e Grow and Block.

Answer 1

Have updated the Wiki-page for AsyncWrapper-Target:
overflowAction - Action to be taken when in-memory-queue becomes full (Reached queueLimit). This means the background-writer is falling behind, and cannot keep up with the application-threads logging. Default: Discard
Possible values:
Discard - The application-thread will discard logevent to avoid becoming blocked or causing out-of-memory issues
Block - The application-thread will block until the background-writer-thread has taken the next batch. Avoids loosing important logevents, but can block all application-threads.
Grow - The application-thread will ignore the limit, and will just allocate more memory. Can cause the entire application to experience out-of-memory-issues.