com.coyotegulch.jisp
Class BTreeIndex

java.lang.Object
  extended bycom.coyotegulch.jisp.BTreeShared
      extended bycom.coyotegulch.jisp.BTreePageFile
          extended bycom.coyotegulch.jisp.BTreeIndex
All Implemented Interfaces:
ObjectIndex

public class BTreeIndex
extends com.coyotegulch.jisp.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

Field Summary
protected  com.coyotegulch.jisp.PageFileHeader m_header
          Header data for a file containing B-Tree pages.
protected  java.util.HashMap m_pageCache
          A cache of pages that have already been loaded into memory.
 
Constructor Summary
BTreeIndex(java.lang.String name)
          Opens an existing file, name, as a BTreeIndex.
BTreeIndex(java.lang.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
 void close()
          Closes an open BTreeIndex and empties the page cache to release memory.
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.
 int count()
          Returns the number of keys stored in this index.
 void dumpTree(java.io.PrintStream output)
          Dumps the entire B-Tree to System.out for analysis.
 void emptyPageCache()
          Empty the page cache.
 long findKey(KeyObject key)
          Find the position of the object associated with a given key.
 long findKey(KeyObject key, boolean allowNext)
          Find the position of an object associated with a given key, or its successor.
 int getPageCacheSize()
          Get the size of the page cache, in number of B-tree pages stored in memory.
 void insertKey(KeyObject key, long reference)
          Insert a key into the index, associating a "reference" value with the given key.
 void removeKey(KeyObject key)
          Removes the given key from the index.
 void replaceKey(KeyObject key, long reference)
          Replaces the reference for the given key.
 void storeKey(KeyObject key, long reference)
          Replaces or inserts the reference for the given key.
 long ticker()
          Returns the number of keys added to this index since its creation.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

m_header

protected com.coyotegulch.jisp.PageFileHeader m_header
Header data for a file containing B-Tree pages.


m_pageCache

protected java.util.HashMap m_pageCache
A cache of pages that have already been loaded into memory. As each page is read

Constructor Detail

BTreeIndex

public BTreeIndex(java.lang.String name)
           throws java.io.IOException,
                  java.lang.ClassNotFoundException
Opens an existing file, name, as a BTreeIndex.

Parameters:
name - name of the external index file to be opened.
Throws:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class
java.lang.ClassNotFoundException - for a casting error, usually when a persistent object or index does match the expected type

BTreeIndex

public BTreeIndex(java.lang.String name,
                  int order,
                  KeyObject nullKey,
                  boolean hasDupes)
           throws java.io.IOException,
                  java.lang.ClassNotFoundException
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:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class
java.lang.ClassNotFoundException - for a casting error, usually when a persistent object or index does match the expected type
See Also:
KeyObject
Method Detail

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

close

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

Throws:
java.io.IOException

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

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

insertKey

public void insertKey(KeyObject key,
                      long reference)
               throws java.io.IOException,
                      java.lang.ClassNotFoundException
Insert a key into the index, associating a "reference" value with the given key.

Specified by:
insertKey in interface ObjectIndex
Parameters:
key - identifies the record to be read
reference - reference associated with key
Throws:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class
java.lang.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

replaceKey

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

Specified by:
replaceKey in interface ObjectIndex
Parameters:
key - identifies the record being replaced
reference - new reference to be associated with key
Throws:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class
java.lang.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)
              throws java.io.IOException,
                     java.lang.ClassNotFoundException
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.

Specified by:
storeKey in interface ObjectIndex
Parameters:
key - identifies the record to be stored
reference - File position of record associated with key
Throws:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class
java.lang.ClassNotFoundException - for a casting error, usually when a persistent object or index does match the expected type
See Also:
KeyObject

findKey

public long findKey(KeyObject key)
             throws java.io.IOException,
                    java.lang.ClassNotFoundException
Find the position of the object associated with a given key.

Specified by:
findKey in interface ObjectIndex
Parameters:
key - a key to be sought in the index
Returns:
Position of the record associated with key.
Throws:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class
java.lang.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)
             throws java.io.IOException,
                    java.lang.ClassNotFoundException
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:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class
java.lang.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

removeKey

public void removeKey(KeyObject key)
               throws java.io.IOException,
                      java.lang.ClassNotFoundException
Removes the given key from the index. If the index contains duplicates of key, the first key found will be deleted.

Specified by:
removeKey in interface ObjectIndex
Parameters:
key - A key identifying the record to be read.
Throws:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class
java.lang.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

emptyPageCache

public void emptyPageCache()
Empty the page cache.


getPageCacheSize

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


dumpTree

public void dumpTree(java.io.PrintStream output)
              throws java.io.IOException,
                     DuplicateKey,
                     java.lang.ClassNotFoundException
Dumps the entire B-Tree to System.out for analysis. For diagnostic purposes only.

Throws:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class
java.lang.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