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java.lang.Objectorg.apache.derby.iapi.store.access.BackingStoreHashtable
A BackingStoreHashtable is a utility class which will store a set of rows into an in memory hash table, or overflow the hash table to a tempory on disk structure.
All rows must contain the same number of columns, and the column at position N of all the rows must have the same format id. If the BackingStoreHashtable needs to be overflowed to disk, then an arbitrary row will be chosen and used as a template for creating the underlying overflow container.
The hash table will be built logically as follows (actual implementation may differ). The important points are that the hash value is the standard java hash value on the row[key_column_numbers[0], if key_column_numbers.length is 1, or row[key_column_numbers[0, 1, ...]] if key_column_numbers.length > 1, and that duplicate detection is done by the standard java duplicate detection provided by java.util.Hashtable.
import java.util.Hashtable; hash_table = new Hashtable(); Object[] row; boolean needsToClone = rowSource.needsToClone(); while((row = rowSource.getNextRowFromRowSource()) != null) { if (needsToClone) row = clone_row_from_row(row); Object key = KeyHasher.buildHashKey(row, key_column_numbers); if ((duplicate_value = hash_table.put(key, row)) != null) { Vector row_vec; // inserted a duplicate if ((duplicate_value instanceof vector)) { row_vec = (Vector) duplicate_value; } else { // allocate vector to hold duplicates row_vec = new Vector(2); // insert original row into vector row_vec.addElement(duplicate_value); // put the vector as the data rather than the row hash_table.put(key, row_vec); } // insert new row into vector row_vec.addElement(row); } }
Field Summary | |
private java.util.Properties |
auxillary_runtimestats
|
private java.util.Hashtable |
hash_table
Fields of the class |
private int[] |
key_column_numbers
|
private boolean |
remove_duplicates
|
private RowSource |
row_source
|
private boolean |
skipNullKeyColumns
|
Constructor Summary | |
private |
BackingStoreHashtable()
Constructors for This class: |
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BackingStoreHashtable(TransactionController tc,
RowSource row_source,
int[] key_column_numbers,
boolean remove_duplicates,
long estimated_rowcnt,
long max_inmemory_rowcnt,
int initialCapacity,
float loadFactor,
boolean skipNullKeyColumns)
Create the BackingStoreHashtable from a row source. |
Method Summary | |
private void |
add_row_to_hash_table(java.util.Hashtable hash_table,
java.lang.Object key,
java.lang.Object[] row)
Do the work to add one row to the hash table. |
private java.lang.Object[] |
cloneRow(java.lang.Object[] old_row)
Return a cloned copy of the row. |
void |
close()
Close the BackingStoreHashtable. |
java.util.Enumeration |
elements()
Return an Enumeration that can be used to scan entire table. |
java.lang.Object |
get(java.lang.Object key)
get data associated with given key. |
void |
getAllRuntimeStats(java.util.Properties prop)
Return runtime stats to caller by adding them to prop. |
private java.lang.Object[] |
getNextRowFromRowSource()
Call method to either get next row or next row with non-null key columns. |
boolean |
put(boolean needsToClone,
java.lang.Object[] row)
Put a row into the hash table. |
java.lang.Object |
remove(java.lang.Object key)
remove a row from the hash table. |
void |
setAuxillaryRuntimeStats(java.util.Properties prop)
Set the auxillary runtime stats. |
int |
size()
Return number of unique rows in the hash table. |
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
private java.util.Hashtable hash_table
private int[] key_column_numbers
private boolean remove_duplicates
private boolean skipNullKeyColumns
private java.util.Properties auxillary_runtimestats
private RowSource row_source
Constructor Detail |
private BackingStoreHashtable()
public BackingStoreHashtable(TransactionController tc, RowSource row_source, int[] key_column_numbers, boolean remove_duplicates, long estimated_rowcnt, long max_inmemory_rowcnt, int initialCapacity, float loadFactor, boolean skipNullKeyColumns) throws StandardException
This routine drains the RowSource. The performance characteristics depends on the number of rows inserted and the parameters to the constructor.
If the number of rows is <= "max_inmemory_rowcnt", then the rows are inserted into a java.util.Hashtable. In this case no TransactionController is necessary, a "null" tc is valid.
If the number of rows is > "max_inmemory_rowcnt", then the rows will be all placed in some sort of Access temporary file on disk. This case requires a valid TransactionController.
tc
- An open TransactionController to be used if the
hash table needs to overflow to disk.row_source
- RowSource to read rows from.key_column_numbers
- The column numbers of the columns in the
scan result row to be the key to the Hashtable.
"0" is the first column in the scan result
row (which may be different than the first
row in the table of the scan).remove_duplicates
- Should the Hashtable automatically remove
duplicates, or should it create the Vector of
duplicates?estimated_rowcnt
- The estimated number of rows in the hash table.
Pass in -1 if there is no estimate.max_inmemory_rowcnt
- The maximum number of rows to insert into the
inmemory Hash table before overflowing to disk.
Pass in -1 if there is no maximum.initialCapacity
- If not "-1" used to initialize the java
Hashtable.loadFactor
- If not "-1" used to initialize the java
Hashtable.skipNullKeyColumns
- Skip rows with a null key column, if true.
StandardException
- Standard exception policy.Method Detail |
private java.lang.Object[] getNextRowFromRowSource() throws StandardException
StandardException
- Standard exception policy.private java.lang.Object[] cloneRow(java.lang.Object[] old_row) throws StandardException
StandardException
- Standard exception policy.private void add_row_to_hash_table(java.util.Hashtable hash_table, java.lang.Object key, java.lang.Object[] row) throws StandardException
row
- Row to add to the hash table.hash_table
- The java HashTable to load into.
StandardException
- Standard exception policy.public void close() throws StandardException
Perform any necessary cleanup after finishing with the hashtable. Will deallocate/dereference objects as necessary. If the table has gone to disk this will drop any on disk files used to support the hash table.
StandardException
- Standard exception policy.public java.util.Enumeration elements() throws StandardException
RESOLVE - is it worth it to support this routine when we have a disk overflow hash table?
StandardException
- Standard exception policy.public java.lang.Object get(java.lang.Object key) throws StandardException
There are 2 different types of objects returned from this routine.
In both cases, the key value is either the object stored in row[key_column_numbers[0]], if key_column_numbers.length is 1, otherwise it is a KeyHasher containing the objects stored in row[key_column_numbers[0, 1, ...]]. For every qualifying unique row value an entry is placed into the Hashtable.
For row values with duplicates, the value of the data is a Vector of rows.
The caller will have to call "instanceof" on the data value object if duplicates are expected, to determine if the data value of the Hashtable entry is a row or is a Vector of rows.
The BackingStoreHashtable "owns" the objects returned from the get() routine. They remain valid until the next access to the BackingStoreHashtable. If the client needs to keep references to these objects, it should clone copies of the objects. A valid BackingStoreHashtable can place all rows into a disk based conglomerate, declare a row buffer and then reuse that row buffer for every get() call.
key
- The key to hash on.
StandardException
- Standard exception policy.public void getAllRuntimeStats(java.util.Properties prop) throws StandardException
prop
- The set of properties to append to.
StandardException
- Standard exception policy.public java.lang.Object remove(java.lang.Object key) throws StandardException
a remove of a duplicate removes the entire duplicate list.
key
- The key of the row to remove.
StandardException
- Standard exception policy.public void setAuxillaryRuntimeStats(java.util.Properties prop) throws StandardException
getRuntimeStats() will return both the auxillary stats and any BackingStoreHashtable() specific stats. Note that each call to setAuxillaryRuntimeStats() overwrites the Property set that was set previously.
prop
- The set of properties to append from.
StandardException
- Standard exception policy.public boolean put(boolean needsToClone, java.lang.Object[] row) throws StandardException
The in memory hash table will need to keep a reference to the row after the put call has returned. If "needsToClone" is true then the hash table will make a copy of the row and put that, else if "needsToClone" is false then the hash table will keep a reference to the row passed in and no copy will be made.
If rouine returns false, then no reference is kept to the duplicate row which was rejected (thus allowing caller to reuse the object).
needsToClone
- does this routine have to make a copy of the row,
in order to keep a reference to it after return?row
- The row to insert into the table.
StandardException
- Standard exception policy.public int size() throws StandardException
StandardException
- Standard exception policy.
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