com.coyotegulch.jisp
public class HashIndex extends Object implements ObjectIndex
Deprecated: As of Jisp versioon 2.5.0, the HashIndex class is deprecated; it will be replaced in Jisp 3.0 by a more efficient and simpler hash-based index.
HashIndex
associates a key
value with a reference to persistent data,
using a disk-based hash table. The index assumes that the position
of a serializable
object is constant, regardless of the actual meaning of the long
position. In
general, the position represents the location (file pointer) of a Serializable
object in an IndexedObjectDatabase
.
Use the IndexedObjectDatabase.attachIndex
method to attach a BTreeIndex
to a database. A database updates all attached indexes when it writes or removes objects
from its file.
This class should not be used in new code. It was originally design to illustrate algorithms, and it suffers from a number of performance problems. A better, more efficient hash-bvased index will be introduced in version 3.0 of Jisp.
See Also: ObjectIndex
Constructor Summary | |
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HashIndex(String name, int numBuckets, int maxRecords, KeyObject nullKey)
Creates the file as a HashIndex . | |
HashIndex(String name)
Opens a file as a HashIndex .
|
Method Summary | |
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void | close() |
long | findKey(KeyObject key)
Find the position of the object associated with a given key.
|
void | insertKey(KeyObject key, long pos)
Insert a key into the database, associating a record position with the given key.
|
void | optimize()
Improves the performance of this HashIndex by optimizing the
index contents.
|
void | removeKey(KeyObject key)
Removes the given key from the index.
|
void | replaceKey(KeyObject key, long pos)
Replace the reference pos for the given key.
|
void | storeKey(KeyObject key, long pos)
If the key already exists, replace the reference pos for the given key. |
HashIndex
. The initial length of each list is
based on numBuckets
and macRecords
. The null key is a "blank" key; obtain
a null key for any KeyObject
type by calling the KeyObject.makeNullKey
method.
Parameters: name The name of the external index file to be opened. numBuckets The number of lists in the hash table; this is also known as the "hash factor."
Use prime numbers to limit the number of collisions and increase the
efficiency of the index. maxRecords The expected number of records to be indexed. This is not
a limit
on the index size; the index will expand to handle up to 2 billion records.
However, the best performance is obtained by setting maxRecords
to a value that reflects the expected size of the database. nullKey The null key serves two purposes: to identify a blank table entry,
and to perform type-checking on new keys added to the index. All
keys added to the index must have the same type as nullkey
.
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type
See Also: KeyObject
HashIndex
.
Parameters: name The name of the external index file to be opened.
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type
Parameters: key A key identifying the record to be read.
Returns: The position of the record associated with key
.
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type KeyNotFound when the specified key can not be found in the index
See Also: KeyNotFound KeyObject
Parameters: key A key identifying the record to be read. pos File position of record associated with key
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type DuplicateKey when inserting a duplicate key into an index that does not support duplicates
See Also: DuplicateKey KeyObject
HashIndex
by optimizing the
index contents.
Parameters: key A key identifying the record to be read.
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type KeyNotFound when the specified key can not be found in the index
See Also: KeyNotFound KeyObject
Parameters: key A key identifying the record to be read. pos File position of record associated with key
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type KeyNotFound when the specified key can not be found in the index
See Also: KeyNotFound KeyObject
Parameters: key A key identifying the record to be read. pos File position of record associated with key
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type
See Also: KeyObject