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/*-
* See the file LICENSE for redistribution information.
*
* Copyright (c) 2009 Oracle. All rights reserved.
*
*/
using System;
using System.Collections.Generic;
using System.Text;
namespace BerkeleyDB {
/// <summary>
/// A class representing configuration parameters for
/// <see cref="HashDatabase"/>
/// </summary>
public class HashDatabaseConfig : DatabaseConfig {
/* Fields for db->set_flags() */
/// <summary>
/// Policy for duplicate data items in the database; that is, insertion
/// when the key of the key/data pair being inserted already exists in
/// the database will be successful.
/// </summary>
/// <remarks>
/// <para>
/// The ordering of duplicates in the database for
/// <see cref="DuplicatesPolicy.UNSORTED"/> is determined by the order
/// of insertion, unless the ordering is otherwise specified by use of a
/// cursor operation or a duplicate sort function. The ordering of
/// duplicates in the database for
/// <see cref="DuplicatesPolicy.SORTED"/> is determined by the
/// duplicate comparison function. If the application does not specify a
/// comparison function using
/// <see cref="DuplicateCompare"/>, a default lexical
/// comparison will be used.
/// </para>
/// <para>
/// <see cref="DuplicatesPolicy.SORTED"/> is preferred to
/// <see cref="DuplicatesPolicy.UNSORTED"/> for performance reasons.
/// <see cref="DuplicatesPolicy.UNSORTED"/> should only be used by
/// applications wanting to order duplicate data items manually.
/// </para>
/// <para>
/// If the database already exists, the value of Duplicates must be the
/// same as the existing database or an error will be returned.
/// </para>
/// </remarks>
public DuplicatesPolicy Duplicates;
internal new uint flags {
get {
uint ret = base.flags;
ret |= (uint)Duplicates;
return ret;
}
}
/// <summary>
/// The policy for how to handle database creation.
/// </summary>
/// <remarks>
/// If the database does not already exist and
/// <see cref="CreatePolicy.NEVER"/> is set,
/// <see cref="HashDatabase.Open"/> will fail.
/// </remarks>
public CreatePolicy Creation;
internal new uint openFlags {
get {
uint flags = base.openFlags;
flags |= (uint)Creation;
return flags;
}
}
/// <summary>
/// The Hash key comparison function.
/// </summary>
/// <remarks>
/// <para>
/// The comparison function is called whenever it is necessary to
/// compare a key specified by the application with a key currently
/// stored in the tree.
/// </para>
/// <para>
/// If no comparison function is specified, the keys are compared
/// lexically, with shorter keys collating before longer keys.
/// </para>
/// <para>
/// If the database already exists, the comparison function must be the
/// same as that historically used to create the database or corruption
/// can occur.
/// </para>
/// </remarks>
public EntryComparisonDelegate HashComparison;
internal bool fillFactorIsSet;
private uint ffactor;
/// <summary>
/// The desired density within the hash table. If no value is specified,
/// the fill factor will be selected dynamically as pages are filled.
/// </summary>
/// <remarks>
/// <para>
/// The density is an approximation of the number of keys allowed to
/// accumulate in any one bucket, determining when the hash table grows
/// or shrinks. If you know the average sizes of the keys and data in
/// your data set, setting the fill factor can enhance performance. A
/// reasonable rule computing fill factor is to set it to the following:
/// </para>
/// <para>
/// (pagesize - 32) / (average_key_size + average_data_size + 8)
/// </para>
/// <para>
/// If the database already exists, this setting will be ignored.
/// </para>
/// </remarks>
public uint FillFactor {
get { return ffactor; }
set {
fillFactorIsSet = true;
ffactor = value;
}
}
/// <summary>
/// A user-defined hash function; if no hash function is specified, a
/// default hash function is used.
/// </summary>
/// <remarks>
/// <para>
/// Because no hash function performs equally well on all possible data,
/// the user may find that the built-in hash function performs poorly
/// with a particular data set.
/// </para>
/// <para>
/// If the database already exists, HashFunction must be the same as
/// that historically used to create the database or corruption can
/// occur.
/// </para>
/// </remarks>
public HashFunctionDelegate HashFunction;
/// <summary>
/// The duplicate data item comparison function.
/// </summary>
/// <remarks>
/// <para>
/// The comparison function is called whenever it is necessary to
/// compare a data item specified by the application with a data item
/// currently stored in the database. Setting DuplicateCompare implies
/// setting <see cref="Duplicates"/> to
/// <see cref="DuplicatesPolicy.SORTED"/>.
/// </para>
/// <para>
/// If no comparison function is specified, the data items are compared
/// lexically, with shorter data items collating before longer data
/// items.
/// </para>
/// <para>
/// If the database already exists when <see cref="HashDatabase.Open"/>
/// is called, the delegate must be the same as that historically used
/// to create the database or corruption can occur.
/// </para>
/// </remarks>
public EntryComparisonDelegate DuplicateCompare;
internal bool nelemIsSet;
private uint nelems;
/// <summary>
/// An estimate of the final size of the hash table.
/// </summary>
/// <remarks>
/// <para>
/// In order for the estimate to be used when creating the database,
/// <see cref="FillFactor"/> must also be set. If the estimate or fill
/// factor are not set or are set too low, hash tables will still expand
/// gracefully as keys are entered, although a slight performance
/// degradation may be noticed.
/// </para>
/// <para>
/// If the database already exists, this setting will be ignored.
/// </para>
/// </remarks>
public uint TableSize {
get { return nelems; }
set {
nelemIsSet = true;
nelems = value;
}
}
/// <summary>
/// Instantiate a new HashDatabaseConfig object
/// </summary>
public HashDatabaseConfig() {
Duplicates = DuplicatesPolicy.NONE;
HashComparison = null;
fillFactorIsSet = false;
nelemIsSet = false;
Creation = CreatePolicy.NEVER;
}
}
}
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