Class HeapCostController

  • All Implemented Interfaces:
    RowCountable, StoreCostController

    public class HeapCostController
    extends GenericCostController
    implements StoreCostController
    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.

    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.

    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.

    The StoreCostController gives 2 kinds of cost information

    • Field Detail

      • num_pages

        long num_pages
        Only lookup these estimates from raw store once.
      • num_rows

        long num_rows
      • page_size

        long page_size
      • row_size

        long row_size
    • Constructor Detail

      • HeapCostController

        public HeapCostController()
    • Method Detail

      • getFetchFromRowLocationCost

        public double getFetchFromRowLocationCost​(FormatableBitSet validColumns,
                                                  int access_type)
                                           throws StandardException
        Return the cost of calling ConglomerateController.fetch().

        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.

        The validColumns describes what kind of row is being fetched, ie. it may be cheaper to fetch a partial row than a complete row.

        Specified by:
        getFetchFromRowLocationCost in interface StoreCostController
        Parameters:
        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".
        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".
        Returns:
        The cost of the fetch.
        Throws:
        StandardException - Standard exception policy.
        See Also:
        RowUtil
      • getScanCost

        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
        Calculate the cost of a scan.

        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.

        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.

        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).

        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.

        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.

        Specified by:
        getScanCost in interface StoreCostController
        Parameters:
        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.
        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.
        group_size - The number of rows to be returned by a single fetch call for STORECOST_SCAN_NORMAL scans.
        forUpdate - Should be true if the caller intends to update through the scan.
        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".
        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.
        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.
        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.
        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.
        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.
        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.
        Throws:
        StandardException - Standard exception policy.
        See Also:
        RowUtil