Class StoredFieldHeader
java.lang.Object
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.
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
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: +--------+-----------------+---------------+------------+ |
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
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Field Summary
FieldsModifier and TypeFieldDescriptionstatic final int
protected static final int
private static final int
Constants of the classstatic final int
private static final int
static final int
static final int
static final int
static final int
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionstatic final boolean
isExtensible
(int status) static final boolean
isFixed
(int status) static final boolean
isNonexistent
(int status) static final boolean
isNull
(int status) Get the status of the field
MT - single thread requiredstatic final boolean
isNullable
(int status) static final boolean
isNullorNonExistent
(int status) static final boolean
isOverflow
(int status) static final boolean
isTagged
(int status) static final int
readFieldDataLength
(ObjectInput in, int status, int fieldDataSize) read the field data lengthstatic final int
readFieldLengthAndSetStreamPosition
(byte[] data, int offset, int status, int fieldDataSize, ArrayInputStream ais) static final int
readStatus
(byte[] page, int offset) static final int
read the field statusstatic final int
readTotalFieldLength
(byte[] data, int offset) read the length of the field and hdr.static final int
setExtensible
(int status, boolean isExtensible) static final int
setFixed
(int status, boolean isFixed) static final int
Set accessors for setting bits in the status field.static final int
setNonexistent
(int status) static final int
setNull
(int status, boolean isNull) static final int
setOverflow
(int status, boolean isOverflow) static final int
setTagged
(int status, boolean isTagged) static final int
size
(int status, int fieldDataLength, int fieldDataSize) static String
toDebugString
(int status) static final int
write
(OutputStream out, int status, int fieldDataLength, int fieldDataSize) write out the field status and field data Length
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Field Details
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FIELD_INITIAL
private static final int FIELD_INITIALConstants of the class- See Also:
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FIELD_NULL
public static final int FIELD_NULL- See Also:
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FIELD_OVERFLOW
public static final int FIELD_OVERFLOW- See Also:
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FIELD_NOT_NULLABLE
private static final int FIELD_NOT_NULLABLE- See Also:
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FIELD_EXTENSIBLE
public static final int FIELD_EXTENSIBLE- See Also:
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FIELD_TAGGED
public static final int FIELD_TAGGED- See Also:
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FIELD_FIXED
protected static final int FIELD_FIXED- See Also:
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FIELD_NONEXISTENT
public static final int FIELD_NONEXISTENT- See Also:
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STORED_FIELD_HEADER_STATUS_SIZE
public static final int STORED_FIELD_HEADER_STATUS_SIZE- See Also:
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Constructor Details
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StoredFieldHeader
public StoredFieldHeader()
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Method Details
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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(OutputStream out, int status, int fieldDataLength, int fieldDataSize) throws IOException write out the field status and field data Length- Throws:
IOException
- Thrown by potential I/O errors while writing field header.
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readStatus
read the field status- Throws:
IOException
- Thrown by potential I/O errors while reading field header.
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readStatus
public static final int readStatus(byte[] page, int offset) -
readTotalFieldLength
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:
IOException
- if an I/O error occurs
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readFieldLengthAndSetStreamPosition
public static final int readFieldLengthAndSetStreamPosition(byte[] data, int offset, int status, int fieldDataSize, ArrayInputStream ais) throws IOException - Throws:
IOException
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readFieldDataLength
public static final int readFieldDataLength(ObjectInput in, int status, int fieldDataSize) throws IOException read the field data length- Throws:
IOException
- Thrown by potential I/O errors while reading field header.
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toDebugString
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