Tomcat 8 throwing - org apache catalina webresources Cache getResource Unable to add the resource

Question

I have just upgraded Tomcat from version 7 0 52 to 8 0 14   I am getting this for lots of static image files      org apache catalina webresources Cache getResource Unable to add the   resource at   base 1325 WA6144-150x112 jpg  to the cache because there   was insufficient free space available after evicting expired cache   entries - consider increasing the maximum size of the cache   I haven t specified any particular resource settings  and I didn t get this for 7 0 52   I have found mention of this happening at startup in a bug report that was supposedly fixed   For me this is happening not at startup but constantly when the resource is requested   Anybody else having this issue   Trying to at least just disable the cache  but I cannot find an example of how to specify not to use the cache   The attributes have gone from the context in Tomcat version 8  Have tried adding a resource but cannot get the config right    lt Resource name  file       cachingAllowed  false      className  org apache catalina webresources FileResourceSet    gt      Thanks

User · Answer

In your  CATALINA BASE conf context xml add block below before  lt  Context gt    lt Resources cachingAllowed  true  cacheMaxSize  100000    gt    For more information  http   tomcat apache org tomcat-8 0-doc config resources html

User · Answer

You have more static resources that the cache has room for  You can do one of the following    Increase the size of the cache Decrease the TTL for the cache Disable caching   For more details see the documentation for these configuration options

User · Answer

This isn   t a solution in the sense that it doesn   t resolve the conditions which cause the message to appear in the logs  but the message can be suppressed by appending the following to conf logging properties   org apache catalina webresources Cache level   SEVERE   This filters out the    Unable to add the resource    logs  which are at level WARNING   In my view a WARNING is not necessarily an error that needs to be addressed  but rather can be ignored if desired

User · Answer

I had the same issue when upgrading from Tomcat 7 to 8  a continuous large flood of log warnings about cache   1  Short Answer  Add this within the Context xml element of your  CATALINA BASE conf context xml    lt  -- The default value is 10240 kbytes  even when not added to context xml  So increase it high enough  until the problem disappears  for example set it to  a value 5 times as high  51200  -- gt   lt Resources cacheMaxSize  51200    gt    So the default is 10240  10 mbyte   so set a size higher than this  Than tune for optimum settings where the warnings disappear  Note that the warnings may come back under higher traffic situations   1 1 The cause  short explanation   The problem is caused by Tomcat being unable to reach its target cache size due to cache entries that are less than the TTL of those entries  So Tomcat didn t have enough cache entries that it could expire  because they were too fresh  so it couldn t free enough cache and thus outputs warnings   The problem didn t appear in Tomcat 7 because Tomcat 7 simply didn t output warnings in this situation   Causing you and me to use poor cache settings without being notified    The problem appears when receiving a relative large amount of HTTP requests for resources  usually static  in a relative short time period compared to the size and TTL of the cache  If the cache is reaching its maximum  10mb by default  with more than 95  of its size with fresh cache entries  fresh means less than less than 5 seconds in cache   than you will get a warning message for each webResource that Tomcat tries to load in the cache   1 2 Optional info  Use JMX if you need to tune cacheMaxSize on a running server without rebooting it   The quickest fix would be to completely disable cache   lt Resources cachingAllowed  false    gt   but that s suboptimal  so increase cacheMaxSize as I just described   2  Long Answer  2 1 Background information  A WebSource is a file or directory in a web application  For performance reasons  Tomcat can cache WebSources  The maximum of the static resource cache  all resources in total  is by default 10240 kbyte  10 mbyte   A webResource is loaded into the cache when the webResource is requested  for example when loading a static image   it s then called a cache entry  Every cache entry has a TTL  time to live   which is the time that the cache entry is allowed to stay in the cache  When the TTL expires  the cache entry is eligible to be removed from the cache  The default value of the cacheTTL is 5000 milliseconds  5 seconds    There is more to tell about caching  but that is irrelevant for the problem   2 2 The cause  The following code from the Cache class shows the caching policy in detail   152     Content will not be cached but we still need metadata size153  long delta   cacheEntry getSize   154  size addAndGet delta  156  if  size get     maxSize   157         Process resources unordered for speed  Trades cache158         efficiency  younger entries may be evicted before older159         ones  for speed since this is on the critical path for160         request processing161      long targetSize  162              maxSize    100 - TARGET FREE PERCENT GET    100 163      long newSize   evict 164              targetSize  resourceCache values   iterator    165      if  newSize   maxSize   166             Unable to create sufficient space for this resource167             Remove it from the cache168          removeCacheEntry path  169          log warn sm getString  cache addFail   path   170       171     When loading a webResource  the code calculates the new size of the cache  If the calculated size is larger than the default maximum size  than one or more cached entries have to be removed  otherwise the new size will exceed the maximum  So the code will calculate a  targetSize   which is the size the cache wants to stay under  as an optimum   which is by default 95  of the maximum  In order to reach this targetSize  entries have to be removed evicted from the cache  This is done using the following code   215  private long evict long targetSize  Iterator lt CachedResource  iter   217      long now   System currentTimeMillis   219      long newSize   size get   221      while  newSize   targetSize  amp  amp  iter hasNext     222          CachedResource resource   iter next   224             Don t expire anything that has been checked within the TTL225          if  resource getNextCheck     now   226              continue 227           229             Remove the entry from the cache230          removeCacheEntry resource getWebappPath    232          newSize   size get   233       235      return newSize 236     So a cache entry is removed when its TTL is expired and the targetSize hasn t been reached yet   After the attempt to free cache by evicting cache entries  the code will do   165  if  newSize   maxSize   166         Unable to create sufficient space for this resource167         Remove it from the cache168      removeCacheEntry path  169      log warn sm getString  cache addFail   path   170     So if after the attempt to free cache  the size still exceeds the maximum  it will show the warning message about being unable to free   cache addFail Unable to add the resource at   0   to the cache for web application   1   because there was insufficient free space available after evicting expired cache entries - consider increasing the maximum size of the cache   2 3 The problem  So as the warning message says  the problem is      insufficient free space available after evicting expired cache entries - consider increasing the maximum size of the cache   If your web application loads a lot of uncached webResources  about maximum of cache  by default 10mb  within a short time  5 seconds   then you ll get the warning   The confusing part is that Tomcat 7 didn t show the warning  This is simply caused by this Tomcat 7 code   1606     Add new entry to cache1607  synchronized  cache   1608         Check cache size  and remove elements if too big1609      if   cache lookup name     null   amp  amp  cache allocate entry size    1610          cache load entry  1611       1612     combined with   231  while  toFree   0   232      if  attempts    maxAllocateIterations   233             Give up  no changes are made to the current cache234          return false 235         So Tomcat 7 simply doesn t output any warning at all when it s unable to free cache  whereas Tomcat 8 will output a warning   So if you are using Tomcat 8 with the same default caching configuration as Tomcat 7  and you got warnings in Tomcat 8  than your  and mine  caching settings of Tomcat 7 were performing poorly without warning   2 4 Solutions  There are multiple solutions    Increase cache  recommended  Lower the TTL  not recommended  Suppress cache log warnings  not recommended  Disable cache   2 4 1  Increase cache  recommended   As described here  http   tomcat apache org tomcat-8 0-doc config resources html  By adding  lt Resources cacheMaxSize  XXXXX    gt  within the Context element in  CATALINA BASE conf context xml  where  XXXXX  stands for an increased cache size  specified in kbytes  The default is 10240  10 mbyte   so set a size higher than this   You ll have to tune for optimum settings  Note that the problem may come back when you suddenly have an increase in traffic resource requests   To avoid having to restart the server every time you want to try a new cache size  you can change it without restarting by using JMX   To enable JMX  add this to  CATALINA BASE conf server xml within the Server element   lt Listener className  org apache catalina mbeans JmxRemoteLifecycleListener  rmiRegistryPortPlatform  6767  rmiServerPortPlatform  6768    gt  and download  catalina-jmx-remote jar from https   tomcat apache org download-80 cgi and put it in  CATALINA HOME lib   Then use jConsole  shipped by default with the Java JDK  to connect over JMX to the server and look through the settings for settings to increase the cache size while the server is running  Changes in these settings should take affect immediately   2 4 2  Lower the TTL  not recommended   Lower the cacheTtl value by something lower than 5000 milliseconds and tune for optimal settings   For example   lt Resources cacheTtl  2000    gt   This comes effectively down to having and filling a cache in ram without using it   2 4 3  Suppress cache log warnings  not recommended   Configure logging to disable the logger for org apache catalina webresources Cache   For more info about logging in Tomcat  http   tomcat apache org tomcat-8 0-doc logging html  2 4 4  Disable cache  You can disable the cache by setting cachingAllowed to false   lt Resources cachingAllowed  false    gt   Although I can remember that in a beta version of Tomcat 8  I was using JMX to disable the cache   Not sure why exactly  but there may be a problem with disabling the cache via server xml

[caching] Tomcat 8 throwing - org.apache.catalina.webresources.Cache.getResource Unable to add the resource

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