JDK-8184994 : Add Dictionary size logging and jcmd
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: runtime
  • Affected Version: 10
  • Priority: P3
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2017-07-20
  • Updated: 2019-05-22
  • Resolved: 2017-08-02
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JDK 10
10 b21Fixed
Related Reports
Relates :  
JDK-7133093 - Improve system dictionary performance
Relates :  
JDK-8185525 - Add JFR event for DictionarySizes
Description
Logging -Xlog:hashtables is currently on for verification but not in production, where you'd want it.  Add logging and jcmd for hashtable sizes.
Comments
Added jcmd <pid> VM.systemdictionary [-verbose] (it is VM.systemdictionary since it's VM.symboltable and VM.stringtable) with output: busaa027.us.oracle.com% jcmd 27918 VM.system_dictionary 27918: System Dictionary for runThese$DirectoryClassLoader statistics: Number of buckets : 107 = 1712 bytes, each 16 Number of entries : 10 = 320 bytes, each 32 Total footprint : = 2032 bytes Average bucket size : 0.093 Variance of bucket size : 0.103 Std. dev. of bucket size: 0.322 Maximum bucket size : 2 System Dictionary for runThese$DirectoryClassLoader statistics: Number of buckets : 107 = 1712 bytes, each 16 Number of entries : 9 = 288 bytes, each 32 Total footprint : = 2000 bytes Average bucket size : 0.084 Variance of bucket size : 0.096 Std. dev. of bucket size: 0.309 Maximum bucket size : 2 ... System Dictionary for <bootloader> statistics: Number of buckets : 1009 = 16144 bytes, each 16 Number of entries : 928 = 29696 bytes, each 32 Total footprint : = 45840 bytes Average bucket size : 0.920 Variance of bucket size : 0.890 Std. dev. of bucket size: 0.944 Maximum bucket size : 5 Placeholder Table statistics: Number of buckets : 1009 = 16144 bytes, each 16 Number of entries : 0 = 0 bytes, each 0 Total footprint : = 16144 bytes Average bucket size : 0.000 Variance of bucket size : 0.000 Std. dev. of bucket size: 0.000 Maximum bucket size : 0 LoaderConstraints Table statistics: Number of buckets : 107 = 1712 bytes, each 16 Number of entries : 7 = 224 bytes, each 32 Total footprint : = 1936 bytes Average bucket size : 0.065 Variance of bucket size : 0.061 Std. dev. of bucket size: 0.247 Maximum bucket size : 1 ProtectionDomainCache Table statistics: Number of buckets : 1009 = 16144 bytes, each 16 Number of entries : 19 = 608 bytes, each 32 Number of literals : 19 = 95 bytes, avg 5.000 Total footprint : = 16847 bytes Average bucket size : 0.019 Variance of bucket size : 0.018 Std. dev. of bucket size: 0.136 Maximum bucket size : 1 SymbolTable and StringTable printing: busaa027.us.oracle.com% jcmd 27918 VM.stringtable 27918: StringTable statistics: Number of buckets : 60013 = 960208 bytes, each 16 Number of entries : 4399 = 140768 bytes, each 32 Number of literals : 4399 = 324912 bytes, avg 73.860 Total footprint : = 1425888 bytes Average bucket size : 0.073 Variance of bucket size : 0.074 Std. dev. of bucket size: 0.272 Maximum bucket size : 3 busaa027.us.oracle.com% jcmd 27918 VM.symboltable 27918: SymbolTable statistics: Number of buckets : 20011 = 320176 bytes, each 16 Number of entries : 31618 = 1011776 bytes, each 32 Number of literals : 31618 = 1427000 bytes, avg 45.133 Total footprint : = 2758952 bytes Average bucket size : 1.580 Variance of bucket size : 1.589 Std. dev. of bucket size: 1.261 Maximum bucket size : 8 Passing -verbose gives the same output as -XX:+PrintSystemDictionaryAtExit
21-07-2017