Apache Derby Database Engine and Embedded JDBC Driver 10.17.1.0 · org.apache.derby.impl.store.raw.data.StoredFieldHeader

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

Modifier and Type	Field and Description
public static final int	FIELD_EXTENSIBLE
protected static final int	FIELD_FIXED
private static final int	FIELD_INITIAL Constants of the class
public static final int	FIELD_NONEXISTENT
private static final int	FIELD_NOT_NULLABLE
public static final int	FIELD_NULL
public static final int	FIELD_OVERFLOW
public static final int	FIELD_TAGGED
public static final int	STORED_FIELD_HEADER_STATUS_SIZE

Constructor Summary

Access	Constructor and Description
public	StoredFieldHeader()

Method Summary

Modifier and Type	Method and Description
public static final boolean	isExtensible(int status)
public static final boolean	isFixed(int status)
public static final boolean	isNonexistent(int status)
public static final boolean	isNull(int status) Get the status of the field MT - single thread required
public static final boolean	isNullable(int status)
public static final boolean	isNullorNonExistent(int status)
public static final boolean	isOverflow(int status)
public static final boolean	isTagged(int status)
public static final int	readFieldDataLength(ObjectInput in, int status, int fieldDataSize) read the field data length
public static final int	readFieldLengthAndSetStreamPosition(byte[] data, int offset, int status, int fieldDataSize, ArrayInputStream ais)
public static final int	readStatus(ObjectInput in) read the field status
public static final int	readStatus(byte[] page, int offset)
public static final int	Returns: The length of the field on the page, including it's header. readTotalFieldLength(byte[] the array where the field is. data, int the offset in the array where the field begin, ie. the status byte is at data[offset]. offset) read the length of the field and hdr.
public static final int	setExtensible(int status, boolean isExtensible)
public static final int	setFixed(int status, boolean isFixed)
public static final int	setInitial() Set accessors for setting bits in the status field.
public static final int	setNonexistent(int status)
public static final int	setNull(int status, boolean isNull)
public static final int	setOverflow(int status, boolean isOverflow)
public static final int	setTagged(int status, boolean isTagged)
public static final int	size(int status, int fieldDataLength, int fieldDataSize)
public static String	toDebugString(int status)
public static final int	write(OutputStream out, int status, int fieldDataLength, int fieldDataSize) write out the field status and field data Length

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll toString wait wait wait

Field Detail

FIELD_EXTENSIBLE	back to summary
public static final int FIELD_EXTENSIBLE

FIELD_FIXED	back to summary
protected static final int FIELD_FIXED

FIELD_INITIAL	back to summary
private static final int FIELD_INITIAL Constants of the class

FIELD_NONEXISTENT	back to summary
public static final int FIELD_NONEXISTENT

FIELD_NOT_NULLABLE	back to summary
private static final int FIELD_NOT_NULLABLE

FIELD_NULL	back to summary
public static final int FIELD_NULL

FIELD_OVERFLOW	back to summary
public static final int FIELD_OVERFLOW

FIELD_TAGGED	back to summary
public static final int FIELD_TAGGED

STORED_FIELD_HEADER_STATUS_SIZE	back to summary
public static final int STORED_FIELD_HEADER_STATUS_SIZE

Constructor Detail

StoredFieldHeader	back to summary
public StoredFieldHeader()

Method Detail

isExtensible	back to summary
public static final boolean isExtensible(int status)

isFixed	back to summary
public static final boolean isFixed(int status)

isNonexistent	back to summary
public static final boolean isNonexistent(int status)

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

isNullable	back to summary
public static final boolean isNullable(int status)

isNullorNonExistent	back to summary
public static final boolean isNullorNonExistent(int status)

isOverflow	back to summary
public static final boolean isOverflow(int status)

isTagged	back to summary
public static final boolean isTagged(int status)

readFieldDataLength	back to summary
public static final int readFieldDataLength(ObjectInput in, int status, int fieldDataSize) throws IOException read the field data length Exceptions IOException: Thrown by potential I/O errors while reading field header.

readFieldDataLength

back to summary

public static final int readFieldDataLength(ObjectInput in, int status, int fieldDataSize) throws IOException

read the field data length

Exceptions

IOException:: Thrown by potential I/O errors while reading field header.

readFieldLengthAndSetStreamPosition	back to summary
public static final int readFieldLengthAndSetStreamPosition(byte[] data, int offset, int status, int fieldDataSize, ArrayInputStream ais) throws IOException

readStatus	back to summary
public static final int readStatus(ObjectInput in) throws IOException read the field status Exceptions IOException: Thrown by potential I/O errors while reading field header.

readStatus

back to summary

public static final int readStatus(ObjectInput in) throws IOException

read the field status

Exceptions

IOException:: Thrown by potential I/O errors while reading field header.

readStatus	back to summary
public static final int readStatus(byte[] page, int offset)

readTotalFieldLength	back to summary
public static final int readTotalFieldLength(byte[] data, int offset) throws 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:byte[] the array where the field is. offset:int the offset in the array where the field begin, ie. the status byte is at data[offset]. Returns:int The length of the field on the page, including it's header. Exceptions IOException: if an I/O error occurs

readTotalFieldLength

back to summary

public static final int readTotalFieldLength(byte[] data, int offset) throws 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:byte[]: the array where the field is.
offset:int: the offset in the array where the field begin, ie. the status byte is at data[offset].

Returns:int

The length of the field on the page, including it's header.

Exceptions

IOException:: if an I/O error occurs

setExtensible	back to summary
public static final int setExtensible(int status, boolean isExtensible)

setFixed	back to summary
public static final int setFixed(int status, boolean isFixed)

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

setNonexistent	back to summary
public static final int setNonexistent(int status)

setNull	back to summary
public static final int setNull(int status, boolean isNull)

setOverflow	back to summary
public static final int setOverflow(int status, boolean isOverflow)

setTagged	back to summary
public static final int setTagged(int status, boolean isTagged)

size	back to summary
public static final int size(int status, int fieldDataLength, int fieldDataSize)

toDebugString	back to summary
public static String toDebugString(int status)

write	back to summary
public static final int write(OutputStream out, int status, int fieldDataLength, int fieldDataSize) throws IOException write out the field status and field data Length Exceptions IOException: Thrown by potential I/O errors while writing field header.

write

back to summary

public static final int write(OutputStream out, int status, int fieldDataLength, int fieldDataSize) throws IOException

write out the field status and field data Length

Exceptions

IOException:: Thrown by potential I/O errors while writing field header.

public final Class StoredFieldHeader

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail