StoredFieldHeader

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org.apache.derby.impl.store.raw.data
Class StoredFieldHeader

java.lang.Object
  org.apache.derby.impl.store.raw.data.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

Field Summary

static int FIELD_EXTENSIBLE


protected static int FIELD_FIXED


private static int FIELD_INITIAL
          Constants of the class

static int FIELD_NONEXISTENT


private static int FIELD_NOT_NULLABLE


static int FIELD_NULL


static int FIELD_OVERFLOW


static int FIELD_TAGGED


static int STORED_FIELD_HEADER_STATUS_SIZE


Constructor Summary

StoredFieldHeader()


Method Summary

static boolean isExtensible(int status)


static boolean isFixed(int status)


static boolean isNonexistent(int status)


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

static boolean isNullable(int status)


static boolean isNullorNonExistent(int status)


static boolean isOverflow(int status)


static boolean isTagged(int status)


static int readFieldDataLength(java.io.ObjectInput in, int status, int fieldDataSize)
          read the field data length

static int readFieldLengthAndSetStreamPosition(byte[] data, int offset, int status, int fieldDataSize, org.apache.derby.iapi.services.io.ArrayInputStream ais)


static int readStatus(byte[] page, int offset)


static int readStatus(java.io.ObjectInput in)
          read the field status

static int readTotalFieldLength(byte[] data, int offset)
          read the length of the field and hdr.

static int setExtensible(int status, boolean isExtensible)


static int setFixed(int status, boolean isFixed)


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

static int setNonexistent(int status)


static int setNull(int status, boolean isNull)


static int setOverflow(int status, boolean isOverflow)


static int setTagged(int status, boolean isTagged)


static int size(int status, int fieldDataLength, int fieldDataSize)


static java.lang.String toDebugString(int status)


static int write(java.io.OutputStream out, int status, int fieldDataLength, int fieldDataSize)
          write out the field status and field data Length

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

FIELD_INITIAL

private static final int FIELD_INITIAL

Constants of the class

See Also:: Constant Field Values

FIELD_NULL

public static final int FIELD_NULL

See Also:: Constant Field Values

FIELD_OVERFLOW

public static final int FIELD_OVERFLOW

See Also:: Constant Field Values

FIELD_NOT_NULLABLE

private static final int FIELD_NOT_NULLABLE

See Also:: Constant Field Values

FIELD_EXTENSIBLE

public static final int FIELD_EXTENSIBLE

See Also:: Constant Field Values

FIELD_TAGGED

public static final int FIELD_TAGGED

See Also:: Constant Field Values

FIELD_FIXED

protected static final int FIELD_FIXED

See Also:: Constant Field Values

FIELD_NONEXISTENT

public static final int FIELD_NONEXISTENT

See Also:: Constant Field Values