com.coyotegulch.jisp

Class BTreeIndex

public class BTreeIndex extends BTreePageFile implements ObjectIndex

Associates a key value with a long reference. In general, the reference is a file pointer that locates a serializable object associated with the key value; however, the index itself does not apply semantics to the reference. The user of index interprets the reference according to its design; an IndexedObjectDatabase, for example, uses the reference to record the file position of a Serializable object with a specific key.

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 is the most common use of BTreeIndexes.

It's important to realize that each key is associated with a long reference which is interpretted by the user. For example, the IndexedObjectDatabase class stores a file pointer in reference, thus associating a key value with a serialized object stored in the database. You can also use the reference as an index into an array, or in any other way appropriate to your application. It is even possible associate the same reference value with different keys.

See Also: ObjectIndex IndexedObjectDatabase

Constructor Summary
BTreeIndex(String name)
Opens an existing file, name, as a BTreeIndex.
BTreeIndex(String name, int order, KeyObject nullKey, boolean hasDupes)
Creates the specified file as a BTreeIndex, using the given order and null key value.
Method Summary
voidclose()
Closes an open BTreeIndex and empties the page cache to release memory.
static intcomputeOrder(int numRecords, int maxHeight)
Calculates a suggested value for a B-tree order, based on a given number of records and a maximum "height" for the B-tree structure.
intcount()
Returns the number of keys stored in this index.
voiddumpTree(PrintStream output)
Dumps the entire B-Tree to System.out for analysis.
voidemptyPageCache()
Empty the page cache.
longfindKey(KeyObject key)
Find the position of the object associated with a given key.
longfindKey(KeyObject key, boolean allowNext)
Find the position of an object associated with a given key, or its successor.
intgetPageCacheSize()
Get the size of the page cache, in number of B-tree pages stored in memory.
voidinsertKey(KeyObject key, long reference)
Insert a key into the index, associating a "reference" value with the given key.
voidremoveKey(KeyObject key)
Removes the given key from the index.
voidreplaceKey(KeyObject key, long reference)
Replaces the reference for the given key.
voidstoreKey(KeyObject key, long reference)
Replaces or inserts the reference for the given key.
longticker()
Returns the number of keys added to this index since its creation.

Constructor Detail

BTreeIndex

public BTreeIndex(String name)
Opens an existing file, name, as a BTreeIndex.

Parameters: name 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

BTreeIndex

public BTreeIndex(String name, int order, KeyObject nullKey, boolean hasDupes)
Creates the specified file as a BTreeIndex, using the given order and null key value. The null key is a "blank" key used in padding empty entries in B-tree pages. Obtain a null key for any key type by either invoking the default constructor or calling the KeyObject.makeNullKey method.

Parameters: name name of the external index file to be opened. order order (page size) the the B-Tree. This should be an odd number greater than or equal to five (5). BTreeIndex will increment any even numbered order to the next consecutive odd number (if you specfy an order of 32, the index will actually have an order of 33). Also, an order less than 5 will be set to 5 automatically. nullKey identifies a blank table entry and provides type-checking on new keys added to the index. All keys added to the index must have the same type as nullkey. hasDupes Determines whether or not this index allows duplicate keys.

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

Method Detail

close

public void close()
Closes an open BTreeIndex and empties the page cache to release memory.

computeOrder

public static int computeOrder(int numRecords, int maxHeight)
Calculates a suggested value for a B-tree order, based on a given number of records and a maximum "height" for the B-tree structure.

Parameters: numRecords number of records expected in a B-tree index maxHeight maximum allowable height for the B-tree (i.e., maximum number of pages to be read when searching for a key)

Returns: a suggested value for oder, to be used in constructing a new BTreeIndex

See Also: BTreeIndex

count

public int count()
Returns the number of keys stored in this index. It is incremented when a new key is added, and decremented when a key is removed.

Returns: the number of keys stored in this index

dumpTree

public void dumpTree(PrintStream output)
Dumps the entire B-Tree to System.out for analysis. For diagnostic purposes only.

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

emptyPageCache

public void emptyPageCache()
Empty the page cache.

findKey

public long findKey(KeyObject key)
Find the position of the object associated with a given key.

Parameters: key a key to be sought in the index

Returns: 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

findKey

public long findKey(KeyObject key, boolean allowNext)
Find the position of an object associated with a given key, or its successor.

Parameters: key a key to be sought in the index allowNext when true, findKey will return the reference associated with the key greater than or equal to key

Returns: The reference 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

getPageCacheSize

public int getPageCacheSize()
Get the size of the page cache, in number of B-tree pages stored in memory.

insertKey

public void insertKey(KeyObject key, long reference)
Insert a key into the index, associating a "reference" value with the given key.

Parameters: key identifies the record to be read reference reference 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

removeKey

public void removeKey(KeyObject key)
Removes the given key from the index. If the index contains duplicates of key, the first key found will be deleted.

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

replaceKey

public void replaceKey(KeyObject key, long reference)
Replaces the reference for the given key. The method replaces the first occurrence of the key, if the index includes duplicates.

Parameters: key identifies the record being replaced reference new reference to be 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: DuplicateKey KeyObject

storeKey

public void storeKey(KeyObject key, long reference)
Replaces or inserts the reference for the given key. If the key exists, the reference associated with that key is replaced; if the key does not exist, a new key is inserted into the database with the given reference. If the index supports duplicate keys, the first-found occurence of the key will be replaced.

Parameters: key identifies the record to be stored position reference 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

ticker

public long ticker()
Returns the number of keys added to this index since its creation. This value is incremented when a new key is added, but (unlike count, it is never decremented. In an index with a one-to-one correspondence between records and keys, this value provides a unique "record ID".

Returns: the number of keys added to this index since its creation