Package org.apache.derby.impl.store.raw.data

Class StoredFieldHeader

  • public final class StoredFieldHeader
extends java.lang.Object
    A class to provide static methods to manipulate fields in the field header. A class StoredPage uses to read/write field status and field data length. No attributes exist in this class, this class provides a set of static methods for writing field status and field data length, and for reading field status and field data length.

    Stored Field Header Format
    The field header is broken into two sections. Only the Status byte is required to be there. 

            Field header format:
        +--------+-------------------+
        | status |  |
        +--------+-------------------+
        Overflow page and overflow id are stored as field data.
        If the overflow bit in status is set, the field data is the overflow 
    information.  When the overflow bit is not set in status, then,
        fieldData is the actually user data for the field.
        That means, field header consists only field status, and field data length.

        A non-overflow field:
        +--------+-------------------+-------------+
        | status |  |  |
        +--------+-------------------+-------------+

        An overflow field:
        +--------+-------------------+-----------------+--------------+
        | status |  |  |  |
        +--------+-------------------+-----------------+--------------+

    status
    The status is 1 byte, it indicates the state of the field. A FieldHeader can be in the following states: NULL - if the field is NULL, no field data length is stored OVERFLOW - indicates the field has been overflowed to another page. overflow page and overflow ID is stored at the end of the user data. field data length must be a number greater or equal to 0, indicating the length of the field that is stored on the current page. The format looks like this: +--------+-----------------+---------------+------------+ ||||| +--------+-----------------+---------------+------------+ overflowPage will be written as compressed long, overflowId will be written as compressed Int NONEXISTENT - the field no longer exists, e.g. column has been dropped during an alter table EXTENSIBLE - the field is of user defined data type. The field may be tagged. TAGGED - the field is TAGGED if and only if it is EXTENSIBLE. FIXED - the field is FIXED if and only if it is used in the log records for version 1.2 and higher.
    fieldDataLength
    The fieldDataLength is only set if the field is not NULL. It is the length of the field that is stored on the current page. The fieldDataLength is a variable length CompressedInt.
    overflowPage and overflowID
    The overflowPage is a variable length CompressedLong, overflowID is a variable Length CompressedInt. They are only stored when the field state is OVERFLOW. And they are not stored in the field header. Instead, they are stored at the end of the field data. The reason we do that is to save a copy if the field has to overflow.
    MT - Mutable - Immutable identity - Thread Aware

    • Constructor Detail

      • StoredFieldHeader

        public StoredFieldHeader()

    • Method Detail

      • isNull

        public static final boolean isNull​(int status)
        Get the status of the field
        MT - single thread required

      • isOverflow

        public static final boolean isOverflow​(int status)

      • isNonexistent

        public static final boolean isNonexistent​(int status)

      • isExtensible

        public static final boolean isExtensible​(int status)

      • isNullorNonExistent

        public static final boolean isNullorNonExistent​(int status)

      • isTagged

        public static final boolean isTagged​(int status)

      • isFixed

        public static final boolean isFixed​(int status)

      • isNullable

        public static final boolean isNullable​(int status)

      • size

        public static final int size​(int status,
                             int fieldDataLength,
                             int fieldDataSize)

      • setInitial

        public static final int setInitial()
        Set accessors for setting bits in the status field.

      • setNull

        public static final int setNull​(int status,
                                boolean isNull)

      • setOverflow

        public static final int setOverflow​(int status,
                                    boolean isOverflow)

      • setNonexistent

        public static final int setNonexistent​(int status)

      • setExtensible

        public static final int setExtensible​(int status,
                                      boolean isExtensible)

      • setTagged

        public static final int setTagged​(int status,
                                  boolean isTagged)

      • setFixed

        public static final int setFixed​(int status,
                                 boolean isFixed)

      • write

        public static final int write​(java.io.OutputStream out,
                              int status,
                              int fieldDataLength,
                              int fieldDataSize)
                       throws java.io.IOException
        write out the field status and field data Length
        Throws:
        java.io.IOException - Thrown by potential I/O errors while writing field header.

      • readStatus

        public static final int readStatus​(java.io.ObjectInput in)
                            throws java.io.IOException
        read the field status
        Throws:
        java.io.IOException - Thrown by potential I/O errors while reading field header.

      • readStatus

        public static final int readStatus​(byte[] page,
                                   int offset)

      • readTotalFieldLength

        public static final int readTotalFieldLength​(byte[] data,
                                             int offset)
                                      throws java.io.IOException
        read the length of the field and hdr.

        Optimized routine used to skip a field on a page. It returns the total length of the field including the header portion. It operates directly on the array and does no checking of it's own for limits on the array length, so an array out of bounds exception may be thrown - the routine is meant to be used to read a field from a page so this should not happen.

        Parameters:
        data - the array where the field is.
        offset - the offset in the array where the field begin, ie. the status byte is at data[offset].
        Returns:
        The length of the field on the page, including it's header.
        Throws:
        java.io.IOException - if an I/O error occurs

      • readFieldLengthAndSetStreamPosition

        public static final int readFieldLengthAndSetStreamPosition​(byte[] data,
                                                            int offset,
                                                            int status,
                                                            int fieldDataSize,
                                                            ArrayInputStream ais)
                                                     throws java.io.IOException
        Throws:
        java.io.IOException

      • readFieldDataLength

        public static final int readFieldDataLength​(java.io.ObjectInput in,
                                            int status,
                                            int fieldDataSize)
                                     throws java.io.IOException
        read the field data length
        Throws:
        java.io.IOException - Thrown by potential I/O errors while reading field header.

      • toDebugString

        public static java.lang.String toDebugString​(int status)