/*

   Derby - Class org.apache.derby.iapi.store.access.StoreCostController

   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to you under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

 */

package org.apache.derby.iapi.store.access;

import org.apache.derby.iapi.types.DataValueDescriptor;

import org.apache.derby.iapi.types.RowLocation;

import org.apache.derby.shared.common.error.StandardException; 
import org.apache.derby.iapi.services.io.FormatableBitSet;

/**

<p>
The StoreCostController interface provides methods that an access client
(most likely the system optimizer) can use to get store's estimated cost of
various operations on the conglomerate the StoreCostController was opened
for.
</p>
<p>
It is likely that the implementation of StoreCostController will open 
the conglomerate and will leave the conglomerate open until the
StoreCostController is closed.  This represents a significant amount of
work, so the caller if possible should attempt to open the StoreCostController
once per unit of work and rather than close and reopen the controller.  For
instance if the optimizer needs to cost 2 different scans against a single
conglomerate, it should use one instance of the StoreCostController.
</p>
<p>
The locking behavior of the implementation of a StoreCostController is
undefined, it may or may not get locks on the underlying conglomerate.  It
may or may not hold locks until end of transaction.  
An optimal implementation will not get any locks on the underlying 
conglomerate, thus allowing concurrent access to the table by a executing
query while another query is optimizing.
</p>

@see TransactionController#openStoreCost
@see RowCountable

**/

public interface StoreCostController extends RowCountable
{
    // The folllowing constants should only be used by StoreCostController
    // implementors.

    // The base cost to fetch a cached page, and select a single
    // heap row by RowLocation, fetching 0 columns.
    public static final double BASE_CACHED_ROW_FETCH_COST = 0.17;

    // The base cost to page in a page from disk to cache, and select a single
    // heap row by RowLocation, fetching 0 columns.
    public static final double BASE_UNCACHED_ROW_FETCH_COST = 1.5;

    // The base cost to fetch a single row as part of group fetch scan with
    // 16 rows per group, fetching 0 columns.
    public static final double BASE_GROUPSCAN_ROW_COST = 0.12;

    // The base cost to fetch a single row as part of a nongroup fetch scan
    // fetching 0 columns.
    public static final double BASE_NONGROUPSCAN_ROW_FETCH_COST = 0.25;

    // The base cost to fetch a single row as part of a nongroup fetch scan
    // fetching 1 columns.
    public static final double BASE_HASHSCAN_ROW_FETCH_COST = 0.14;


    // This is an estimate of the per byte cost associated with fetching the 
    // row from the table, it just assumes the cost scales per byte which is 
    // probably not true, but a good first guess.  It is meant to be added
    // to the above costs - for instance the cost of fetching a 100 byte 
    // row from a page assumed to be in the cache is:
    //     BASE_CACHED_ROW_FETCH_COST + (100 * BASE_ROW_PER_BYTECOST)
    //
    // The estimate for this number is the cost of retrieving all cost from
    // a cached 100 byte row - the cost of getting 0 colums from cached row.
    public static final double BASE_ROW_PER_BYTECOST = (0.56 - 0.16) / 100;

    /**
     * Indicates that access to the page necessary to fulfill the fetch
     * request is likely to be a page "recently" used.  See 
     * getFetchFromFullKeyCost() and getScanCost().
     **/
    public static final int STORECOST_CLUSTERED = 0x01;

    /**
     * Used for the scan_type parameter to the getScanCost() routine.
     * STORECOST_SCAN_NORMAL indicates that the scan will use the standard 
     * next/fetch, where each fetch can retrieve 1 or many rows (if 
     * fetchNextGroup() interface is used).
     **/
    public static final int STORECOST_SCAN_SET      = 0x01;


    /**
     * Used for the scan_type parameter to the getScanCost() routine.
     * STORECOST_SCAN_SET - The entire result set will be retrieved using the
     * the fetchSet() interface.
     **/
    public static final int STORECOST_SCAN_NORMAL   = 0x02;

    /**
     * Close the controller.
     * <p>
     * Close the open controller.  This method always succeeds, and never 
     * throws any exceptions. Callers must not use the StoreCostController 
     * Cost controller after closing it; they are strongly advised to clear
     * out the scan controller reference after closing.
     * <p>
     *
	 * @exception  StandardException  Standard exception policy.
     **/
    void close()
        throws StandardException;

    /**
     * Return the cost of calling ConglomerateController.fetch().
     * <p>
     * Return the estimated cost of calling ConglomerateController.fetch()
     * on the current conglomerate.  This gives the cost of finding a record
     * in the conglomerate given the exact RowLocation of the record in
     * question. 
     * <p>
     * The validColumns parameter describe what kind of row 
     * is being fetched, ie. it may be cheaper to fetch a partial row than a 
     * complete row.
     * <p>
     *
     *
	 * @param validColumns    A description of which columns to return from
     *                        row on the page into "templateRow."  templateRow,
     *                        and validColumns work together to
     *                        describe the row to be returned by the fetch - 
     *                        see RowUtil for description of how these three 
     *                        parameters work together to describe a fetched 
     *                        "row".
     *
     * @param access_type     Describe the type of access the query will be
     *                        performing to the ConglomerateController.  
     *
     *                        STORECOST_CLUSTERED - The location of one fetch
     *                            is likely clustered "close" to the next 
     *                            fetch.  For instance if the query plan were
     *                            to sort the RowLocations of a heap and then
     *                            use those RowLocations sequentially to 
     *                            probe into the heap, then this flag should
     *                            be specified.  If this flag is not set then
     *                            access to the table is assumed to be
     *                            random - ie. the type of access one gets 
     *                            if you scan an index and probe each row
     *                            in turn into the base table is "random".
     *
     *
	 * @return The cost of the fetch.
     *
	 * @exception  StandardException  Standard exception policy.
     *
	 * @see RowUtil
     **/
    public double getFetchFromRowLocationCost(
    FormatableBitSet     validColumns,
    int         access_type)
		throws StandardException;

    /**
     * Return the cost of exact key lookup.
     * <p>
     * Return the estimated cost of calling ScanController.fetch()
     * on the current conglomerate, with start and stop positions set such
     * that an exact match is expected.
     * <p>
     * This call returns the cost of a fetchNext() performed on a scan which
     * has been positioned with a start position which specifies exact match
     * on all keys in the row.
     * <p>
     * Example:
     * <p>
     * In the case of a btree this call can be used to determine the cost of
     * doing an exact probe into btree, giving all key columns.  This cost
     * can be used if the client knows it will be doing an exact key probe
     * but does not have the key's at optimize time to use to make a call to
     * getScanCost()
     * <p>
     *
     *
	 * @param validColumns    A description of which columns to return from
     *                        row on the page into "templateRow."  templateRow,
     *                        and validColumns work together to
     *                        describe the row to be returned by the fetch - 
     *                        see RowUtil for description of how these three 
     *                        parameters work together to describe a fetched 
     *                        "row".
     *
     * @param access_type     Describe the type of access the query will be
     *                        performing to the ScanController.  
     *
     *                        STORECOST_CLUSTERED - The location of one scan
     *                            is likely clustered "close" to the previous 
     *                            scan.  For instance if the query plan were
     *                            to used repeated "reopenScan()'s" to probe
     *                            for the next key in an index, then this flag
     *                            should be be specified.  If this flag is not 
     *                            set then each scan will be costed independant
     *                            of any other predicted scan access.
     *
	 * @return The cost of the fetch.
     *
	 * @exception  StandardException  Standard exception policy.
     *
	 * @see RowUtil
     **/
    public double getFetchFromFullKeyCost(
    FormatableBitSet     validColumns,
    int         access_type)
		throws StandardException;

    /**
     * Calculate the cost of a scan.
     * <p>
     * Cause this object to calculate the cost of performing the described
     * scan.  The interface is setup such that first a call is made to
     * calcualteScanCost(), and then subsequent calls to accessor routines
     * are made to get various pieces of information about the cost of
     * the scan.
     * <p>
     * For the purposes of costing this routine is going to assume that 
     * a page will remain in cache between the time one next()/fetchNext()
     * call and a subsequent next()/fetchNext() call is made within a scan.
     * <p>
     * The result of costing the scan is placed in the "cost_result".  
     * The cost of the scan is stored by calling 
     * cost_result.setEstimatedCost(cost).
     * The estimated row count is stored by calling 
     * cost_result.setEstimatedRowCount(row_count).
     * <p>
     * The estimated cost of the scan assumes the caller will 
     * execute a fetchNext() loop for every row that qualifies between
     * start and stop position.  Note that this cost is different than
     * execution a next(),fetch() loop; or if the scan is going to be
     * terminated by client prior to reaching the stop condition.
     * <p>
     * The estimated number of rows returned from the scan 
     * assumes the caller will execute a fetchNext() loop for every 
     * row that qualifies between start and stop position.
     * <p>
     *
     *
     * @param scan_type       The type of scan that will be executed.  There
     *                        are currently 2 types:
     *                        STORECOST_SCAN_NORMAL - scans will be executed
     *                        using the standard next/fetch, where each fetch
     *                        can retrieve 1 or many rows (if fetchNextGroup()
     *                        interface is used).
     *
     *                        STORECOST_SCAN_SET - The entire result set will
     *                        be retrieved using the the fetchSet() interface.
     *
     * @param row_count       Estimated total row count of the table.  The 
     *                        current system tracks row counts in heaps better
     *                        than btree's (btree's have "rows" which are not
     *                        user rows - branch rows, control rows), so 
     *                        if available the client should
     *                        pass in the base table's row count into this
     *                        routine to be used as the index's row count.
     *                        If the caller has no idea, pass in -1.
     *
     * @param group_size      The number of rows to be returned by a single
     *                        fetch call for STORECOST_SCAN_NORMAL scans.
     *
	 * @param forUpdate       Should be true if the caller intends to update 
     *                        through the scan.
     * 
	 * @param scanColumnList  A description of which columns to return from 
     *                        every fetch in the scan.  template, 
     *                        and scanColumnList work together
     *                        to describe the row to be returned by the scan - 
     *                        see RowUtil for description of how these three 
     *                        parameters work together to describe a "row".
     * 
     * @param template        A prototypical row which the scan may use to
	 *                        maintain its position in the conglomerate.  Not 
     *                        all access method scan types will require this, 
     *                        if they don't it's ok to pass in null.
     *                        In order to scan a conglomerate one must 
     *                        allocate 2 separate "row" templates.  The "row" 
     *                        template passed into openScan is for the private
     *                        use of the scan itself, and no access to it
     *                        should be made by the caller while the scan is 
     *                        still open.  Because of this the scanner must 
     *                        allocate another "row" template to hold the 
     *                        values returned from fetch().  Note that this 
     *                        template must be for the full row, whether a 
     *                        partial row scan is being executed or not.
     *
	 * @param startKeyValue   An indexable row which holds a (partial) key 
     *                        value which, in combination with the 
     *                        startSearchOperator, defines the starting 
     *                        position of the scan.  If null, the starting
     *                        position of the scan is the first row of the 
     *                        conglomerate.  The startKeyValue must only
     *                        reference columns included in the scanColumnList.
     *
	 * @param startSearchOperator 
     *                        an operator which defines how the startKeyValue
     *                        is to be searched for.  If startSearchOperation 
     *                        is ScanController.GE, the scan starts on the 
     *                        first row which is greater than or equal to the 
	 *                        startKeyValue.  If startSearchOperation is 
     *                        ScanController.GT, the scan starts on the first
     *                        row whose key is greater than startKeyValue.  The
     *                        startSearchOperation parameter is ignored if the
     *                        startKeyValue parameter is null.
     *
	 * @param stopKeyValue    An indexable row which holds a (partial) key 
     *                        value which, in combination with the 
     *                        stopSearchOperator, defines the ending position
     *                        of the scan.  If null, the ending position of the
     *                        scan is the last row of the conglomerate.  The
     *                        stopKeyValue must only reference columns included
     *                        in the scanColumnList.
     *
	 * @param stopSearchOperator
     *                        an operator which defines how the stopKeyValue
     *                        is used to determine the scan stopping position. 
     *                        If stopSearchOperation is ScanController.GE, the
     *                        scan stops just before the first row which is
     *                        greater than or equal to the stopKeyValue.  If 
     *                        stopSearchOperation is ScanController.GT, the 
     *                        scan stops just before the first row whose key 
     *                        is greater than startKeyValue.  The
     *                        stopSearchOperation parameter is ignored if the
     *                        stopKeyValue parameter is null.
     *
     *                        
     * @param access_type     Describe the type of access the query will be
     *                        performing to the ScanController.  
     *
     *                        STORECOST_CLUSTERED - The location of one scan
     *                            is likely clustered "close" to the previous 
     *                            scan.  For instance if the query plan were
     *                            to used repeated "reopenScan()'s" to probe
     *                            for the next key in an index, then this flag
     *                            should be be specified.  If this flag is not 
     *                            set then each scan will be costed independant
     *                            of any other predicted scan access.
     *
     *
	 * @exception  StandardException  Standard exception policy.
     *
	 * @see RowUtil
     **/
	public void getScanCost(
        int                     scan_type,
        long                    row_count,
        int                     group_size,
		boolean                 forUpdate,
		FormatableBitSet                 scanColumnList,
		DataValueDescriptor[]   template,
		DataValueDescriptor[]   startKeyValue,
		int                     startSearchOperator,
		DataValueDescriptor[]   stopKeyValue,
		int                     stopSearchOperator,
        boolean                 reopen_scan,
        int                     access_type,
        StoreCostResult         cost_result)
			throws StandardException;

    /**
     * Return an "empty" row location object of the correct type.
     * <p>
     *
	 * @return The empty Rowlocation.
     *
	 * @exception  StandardException  Standard exception policy.
     **/
	RowLocation newRowLocationTemplate()
		throws StandardException;
}
