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

Fields

Modifier and Type	Field and Description
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

Constructors

Constructor and Description
StoredFieldHeader()

Method Summary

Modifier and Type	Method and Description
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, 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

STORED_FIELD_HEADER_STATUS_SIZE

public static final int STORED_FIELD_HEADER_STATUS_SIZE

See Also:

Constant Field Values

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)