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 Description static int
FIELD_EXTENSIBLE
protected static int
FIELD_FIXED
private static int
FIELD_INITIAL
Constants of the classstatic 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 Description StoredFieldHeader()
-
Method Summary
All Methods Static Methods Concrete Methods Modifier and Type Method 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 requiredstatic 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 lengthstatic 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 statusstatic 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
-
-
-
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
-
-
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)
-
-