Difference between revisions of "MemoryAnalyzer/Indexes"

Latest revision as of 04:26, 28 May 2021

Index

Memory Analyzer uses several indexes to enable access to different parts of the snapshot.

IDENTIFIER 

IntToLong - object ID to object address

O2CLASS 

object ID to class ID

A2SIZE 

array object ID (or other non-fixed size object) to encoded size (32-bits)

INBOUND 

object ID to list of object IDs

OUTBOUND 

object ID to list of object IDs

DOMINATED 

Dominated: object id to N dominated object ids

O2RETAINED 

object ID to long

DOMINATOR 

Dominator of: object id to the id of its dominator

I2RETAINED 

cache of size of class, classloader (read/write)

IntIndexReader

For an index file like O2CLASS, the file is stored as many ArrayIntCompressed followed by an index: IntIndexReader There is a special adjustment to cope with >2^31 entries files as that can be needed for 1 to N files. On reading there is a SoftReference cache of those ArrayIntCompressed pages. The data is read using a SimpleBufferedRandomAccessInputStream which just has local buffer.

LongIndexReader

LongIndexReader is similar (without the adjustment for 2^31 entries)

PositionIndexReader

PositionIndexReader is similar (without the adjustment for 2^31 entries)

1 to N reader

IntIndex1NReader Has two parts, a body and an header, and a final long of the position of the split in the file. For an input, use the header to find the position of the start in the body and the header via (index+1) to find the position of the next entry. Read data between the two from the body

Random Access File caching

HPROF random access to GZIP compressed files to read fields and array contents

• org.eclipse.mat.hprof.DefaultPositionInputStream
  • org.eclipse.mat.parser.io.BufferedRandomAccessInputStream
    • HashMapLongObject
      • [*N] page
        • [*N] SoftReference
          • buffer byte[512]
    • org.eclipse.mat.hprof.CompressedRandomAccessFile
      • org.eclipse.mat.hprof.SeekableStream
        • [*N} org.eclipse.mat.hprof.SeekableStream$PosStream
          • SoftReference
            • org.eclipse.mat.hprof.GZIPInputStream2
              • io.nayuki.deflate.InflaterInputStream
                • inputBuffer byte[16384]
                • dictionary byte[32768]