Package org.apache.jackrabbit.oak.segment.data

Interface SegmentData

  • public interface SegmentData
    Access the data of a segment.

    A segment is composed of a header and the proper data. The header has a fixed- and a variable-length part.

    The fixed-length part of the header contains a signature, which is a string that uniquely identifies the rest of the content as a segment; a getVersion(), which specifies the version of the binary format used to serialize the content of the segment; a full generation, which describes the generation of the segment with regards to full compaction; a generation, which identifies the generation of the segment with regards to full or tail compaction; a compacted flag, which determines if the segment was written by a compaction operation; the number of record references, which is the number of record entries in the segment; the number of segment references, which is the number of identifiers of other segments used by this segment.

    The variable part of the header contains the list of segment references and the list of record references. A segment references is composed by the most significant bits and lsb of the segment identifier. A record reference is composed of a record number, a record type and a record offset.

    The most prominent use for a segment is to hold record data. Many methods of this class allows access to the record data. These methods accept an integer representing an absolute position pointing to the record data. The absolute position, though, is virtual: it is computed on a virtual segment 256K long. This offset is usually obtained by accessing the record offset of a record reference entry. The class will normalize the offset for the actual size of the segment, which can be smaller than 256K. It is acceptable to displace the offset of a record reference entry by a positive amount. This can be useful to access a field of a composite record saved at a specific offset.

    • Method Detail

      • getVersion

        byte getVersion()

      • getSignature

        String getSignature()

      • getFullGeneration

        int getFullGeneration()

      • isCompacted

        boolean isCompacted()

      • getGeneration

        int getGeneration()

      • getSegmentReferencesCount

        int getSegmentReferencesCount()

      • getRecordReferencesCount

        int getRecordReferencesCount()

      • getRecordReferenceNumber

        int getRecordReferenceNumber​(int i)

      • getRecordReferenceType

        byte getRecordReferenceType​(int i)

      • getRecordReferenceOffset

        int getRecordReferenceOffset​(int i)

      • getSegmentReferenceMsb

        long getSegmentReferenceMsb​(int i)

      • getSegmentReferenceLsb

        long getSegmentReferenceLsb​(int i)

      • readLength

        default long readLength​(int recordReferenceOffset)

      • readString

        default StringData readString​(int recordReferenceOffset)

      • readRecordId

        default RecordIdData readRecordId​(int recordReferenceOffset)

      • readByte

        byte readByte​(int recordReferenceOffset)

      • readInt

        int readInt​(int recordReferenceOffset)

      • readShort

        short readShort​(int recordReferenceOffset)

      • readLong

        long readLong​(int recordReferenceOffset)

      • readBytes

        Buffer readBytes​(int recordReferenceOffset,
                 int size)

      • size

        int size()

      • estimateMemoryUsage

        int estimateMemoryUsage()