/**
* Remove an entry with the given key from the BTree.
*
* @param key Removal key
* @return Value associated with the key, or null if no entry with given key existed in the BTree.
*/
public synchronized Object remove(Object key) throws IOException {
if (key == null) {
throw new IllegalArgumentException("Argument 'key' is null");
}
BPage rootPage = getRoot();
if (rootPage == null) {
return null;
}
boolean dirty = false;
BPage.RemoveResult remove = rootPage.remove(_height, key);
if (remove._underflow && rootPage.isEmpty()) {
_height -= 1;
dirty = true;
// TODO: check contract for BPages to be removed from recman.
if (_height == 0) {
_root = 0;
} else {
_root = rootPage.childBPage(_pageSize - 1)._recid;
}
}
if (remove._value != null) {
_entries--;
dirty = true;
}
if (dirty) {
_recman.update(_recid, this);
}
return remove._value;
}
/**
* Load a persistent BTree.
*
* @param recman RecordManager used to store the persistent btree
* @param recid Record id of the BTree
*/
public static BTree load(RecordManager recman, long recid) throws IOException {
BTree btree = (BTree) recman.fetch(recid);
btree._recid = recid;
btree._recman = recman;
btree._bpageSerializer = new BPage();
btree._bpageSerializer._btree = btree;
return btree;
}
/**
* Insert an entry in the BTree.
*
* <p>The BTree cannot store duplicate entries. An existing entry can be replaced using the <code>
* replace</code> flag. If an entry with the same key already exists in the BTree, its value is
* returned.
*
* @param key Insert key
* @param value Insert value
* @param replace Set to true to replace an existing key-value pair.
* @return Existing value, if any.
*/
public synchronized Object insert(Object key, Object value, boolean replace) throws IOException {
if (key == null) {
throw new IllegalArgumentException("Argument 'key' is null");
}
if (value == null) {
throw new IllegalArgumentException("Argument 'value' is null");
}
BPage rootPage = getRoot();
if (rootPage == null) {
// BTree is currently empty, create a new root BPage
if (DEBUG) {
System.out.println("BTree.insert() new root BPage");
}
rootPage = new BPage(this, key, value);
_root = rootPage._recid;
_height = 1;
_entries = 1;
_recman.update(_recid, this);
return null;
} else {
BPage.InsertResult insert = rootPage.insert(_height, key, value, replace);
boolean dirty = false;
if (insert._overflow != null) {
// current root page overflowed, we replace with a new root page
if (DEBUG) {
System.out.println("BTree.insert() replace root BPage due to overflow");
}
rootPage = new BPage(this, rootPage, insert._overflow);
_root = rootPage._recid;
_height += 1;
dirty = true;
}
if (insert._existing == null) {
_entries++;
dirty = true;
}
if (dirty) {
_recman.update(_recid, this);
}
// insert might have returned an existing value
return insert._existing;
}
}
/** Return the root BPage, or null if it doesn't exist. */
private BPage getRoot() throws IOException {
if (_root == 0) {
return null;
}
BPage root = (BPage) _recman.fetch(_root, _bpageSerializer);
root._recid = _root;
root._btree = this;
return root;
}
/**
* Create a new persistent BTree with the given number of entries per node.
*
* @param recman Record manager used for persistence.
* @param comparator Comparator used to order index entries
* @param keySerializer Serializer used to serialize index keys (optional)
* @param valueSerializer Serializer used to serialize index values (optional)
* @param pageSize Number of entries per page (must be even).
*/
public static BTree createInstance(
RecordManager recman,
Comparator comparator,
Serializer keySerializer,
Serializer valueSerializer,
int pageSize)
throws IOException {
BTree btree;
if (recman == null) {
throw new IllegalArgumentException("Argument 'recman' is null");
}
if (comparator == null) {
throw new IllegalArgumentException("Argument 'comparator' is null");
}
if (!(comparator instanceof Serializable)) {
throw new IllegalArgumentException("Argument 'comparator' must be serializable");
}
if (keySerializer != null && !(keySerializer instanceof Serializable)) {
throw new IllegalArgumentException("Argument 'keySerializer' must be serializable");
}
if (valueSerializer != null && !(valueSerializer instanceof Serializable)) {
throw new IllegalArgumentException("Argument 'valueSerializer' must be serializable");
}
// make sure there's an even number of entries per BPage
if ((pageSize & 1) != 0) {
throw new IllegalArgumentException("Argument 'pageSize' must be even");
}
btree = new BTree();
btree._recman = recman;
btree._comparator = comparator;
btree._keySerializer = keySerializer;
btree._valueSerializer = valueSerializer;
btree._pageSize = pageSize;
btree._bpageSerializer = new BPage();
btree._bpageSerializer._btree = btree;
btree._recid = recman.insert(btree);
return btree;
}