Package org.apache.derby.impl.services.daemon

Class IndexStatisticsDaemonImpl

  • All Implemented Interfaces:
    java.lang.Runnable, IndexStatisticsDaemon
    public class IndexStatisticsDaemonImpl
extends java.lang.Object
implements IndexStatisticsDaemon, java.lang.Runnable
    Daemon acting as a coordinator for creating and updating index cardinality statistics.

    The need for updated statistics is currently determined when compiling a SELECT query. The unit of work is then scheduled with this daemon, and the work itself will be carried out in a separate thread. If the worker thread doesn't exist it is created, if it is idle the unit of work will be processed immediately, and if it is busy the unit of work has to wait in the queue.

    The daemon code has a notion of a background task. If the update is run as a background task, it will try to affect other activity in the Derby database as little as possible. As far as possible, it will not set locks on the conglomerates it scans, and if it needs to take locks it will give up immediately if the locks cannot be obtained. In some cases it will also roll back to release locks already taken, ad then retry. Since we are accessing shared structures the background work may still interfere with the user activity in the database due to locking, but all such operations carried out by the daemon are of short duration.

    The high level flow of an update to index statistics is:

    1. schedule update (the only action carried out by the user thread)
    3. for each index:
      1. scan index
      2. invalidate statements dependent on current statistics
      3. drop existing statistics
      4. add new statistics

    List of possible improvements:

    1. Reduce potential impact of multiple invalidations (per table), probably by finding a way to invalidate only once after all indexes for a table have had their statistics updated. So far invalidation has proven to be the most difficult piece of the puzzle due to the interaction with the data dictionary and sensitivity to concurrent activity for the table.

    Implementation notes: List of potential cleanups before going into a release:

    1. Consider removing all tracing code. May involve improving logging if parts of the trace output is valuable enough.

    • Field Detail

      • MAX_QUEUE_LENGTH

        private static final int MAX_QUEUE_LENGTH
        Maximum number of work units allowed in the queue.

      • doLog

        private final boolean doLog
        Tells if logging is enabled.

      • doTrace

        private final boolean doTrace
        Tells if tracing is enabled.

      • traceToDerbyLog

        private final boolean traceToDerbyLog
        Tells if traces are written to the Derby log file.

      • traceToStdOut

        private final boolean traceToStdOut
        Tells if traces are written to standard out.

      • daemonDisabled

        private boolean daemonDisabled
        Tells if the daemon has been disabled.

      • ctxMgr

        private final ContextManager ctxMgr
        The context manager for the worker thread.

      • skipDisposableStats

        public final boolean skipDisposableStats
        Tells if disposable stats should be generated, which will happen in soft-upgrade mode or when the user asks us to revert to the old behavior.

        Made public to allow access for CreateIndexConstantAction and FromBaseTable, but this is no longer necessary when the debug property to keep disposable statistics is removed.

      • db

        private final Database db
        The database object for the database we are handling automatic index statistics update for.

      • dbOwner

        private final java.lang.String dbOwner
        The name of the database owner.

      • databaseName

        private final java.lang.String databaseName

      • queue

        private final java.util.ArrayList<TableDescriptor> queue
        A list of tables that shall have their index statistics updated. Note that the descriptor isn't removed before the work has been completed.

      • runningThread

        private java.lang.Thread runningThread
        The thread in which the index statistics refresh operation is being executed, if any. Created as needed, but there will only be one thread doing the work. The thread is allowed to die since it is assumed that index statistics regeneration is rather infrequent.

      • errorsConsecutive

        private int errorsConsecutive
        Number of consecutive errors, used as a metric to decide if the damoen should be automatically shut down.

      • errorsUnknown

        private long errorsUnknown

      • errorsKnown

        private long errorsKnown

      • wuProcessed

        private long wuProcessed

      • wuScheduled

        private long wuScheduled

      • wuRejectedDup

        private long wuRejectedDup

      • wuRejectedFQ

        private long wuRejectedFQ

      • wuRejectedOther

        private long wuRejectedOther

      • timeOfCreation

        private final long timeOfCreation
        Specifies when the daemon was created.

      • runTime

        private long runTime
        The period of time (ms) for which the daemon has been doing active work.

      • tsb

        private final java.lang.StringBuffer tsb

    • Constructor Detail

      • IndexStatisticsDaemonImpl

        public IndexStatisticsDaemonImpl​(HeaderPrintWriter log,
                                 boolean doLog,
                                 java.lang.String traceLevel,
                                 Database db,
                                 java.lang.String userName,
                                 java.lang.String databaseName)
        Creates a new daemon.
        Parameters:
        log - the log to write to
        doLog - whether to log activity information
        traceLevel - whether, and to where, trace information should be written ("off|log|stdout|both")
        db - the database ("off|log|stdout|both")
        userName - the name of the database owner
        databaseName - the name of the database (not stored in the db obj)

    • Method Detail

      • dbAtLeast10_9

        private boolean dbAtLeast10_9​(Database db)
        Tells if the database is 10.9 or newer.

      • schedule

        public void schedule​(TableDescriptor td)
        Schedules an update of the index statistics for the specified table.

        Assume the descriptor will be valid until we get around to generate the statistics. If it turns out to be invalid, it will be discarded.

        Specified by:
        schedule in interface IndexStatisticsDaemon
        Parameters:
        td - base table descriptor to update index statistics for

      • acceptWork

        private boolean acceptWork​(TableDescriptor td)
        Determines if the given work can be accepted.
        Parameters:
        td - the table descriptor to check
        Returns:
        true if work can be accepted, false if not.

      • generateStatistics

        private void generateStatistics​(LanguageConnectionContext lcc,
                                TableDescriptor td)
                         throws StandardException
        Generates index statistics for all indexes associated with the given table descriptor.

        This method is run as a background task.

        Parameters:
        lcc - connection context to use to perform the work
        td - target base table descriptor
        Throws:
        StandardException - if accessing the conglomerates fail

      • isShuttingDown

        private boolean isShuttingDown()
        Return true if we are being shutdown

      • updateIndexStatsMinion

        private void updateIndexStatsMinion​(LanguageConnectionContext lcc,
                                    TableDescriptor td,
                                    ConglomerateDescriptor[] cds,
                                    boolean asBackgroundTask)
                             throws StandardException
        Updates the index statistics for the given table and the specified indexes.

        API note: Using null to update the statistics for all conglomerates is preferred over explicitly passing an array with all the conglomerates for the table. Doing so allows for some optimizations, and will cause a disposable statistics check to be performed.

        Parameters:
        lcc - language connection context used to perform the work
        td - the table to update index stats for
        cds - the conglomerates to update statistics for (non-index conglomerates will be ignored), null means all indexes
        asBackgroundTask - whether the updates are done automatically as part of a background task or if explicitly invoked by the user
        Throws:
        StandardException - if something goes wrong

      • writeUpdatedStats

        private void writeUpdatedStats​(LanguageConnectionContext lcc,
                               TableDescriptor td,
                               UUID index,
                               long numRows,
                               long[] cardinality,
                               boolean asBackgroundTask)
                        throws StandardException
        Writes updated statistics for the specified index to the data dictionary.
        Parameters:
        lcc - connection context to use to perform the work
        td - the base table
        index - the index of the base table
        numRows - number of rows in the base table
        cardinality - the number of unique values in the index (per number of leading columns)
        asBackgroundTask - whether the update is done automatically as part of a background task or if explicitly invoked by the user
        Throws:
        StandardException - if updating the data dictionary fails

      • invalidateStatements

        private void invalidateStatements​(LanguageConnectionContext lcc,
                                  TableDescriptor td,
                                  boolean asBackgroundTask)
                           throws StandardException
        Performs an invalidation action for the given table (the event being statistics update).
        Parameters:
        lcc - connection context to use to perform the work
        td - the table to invalidate for
        asBackgroundTask - whether the update is done automatically as part of a background task or if explicitly invoked by the user
        Throws:
        StandardException - if the invalidation request fails

      • setHeapRowEstimate

        private void setHeapRowEstimate​(TransactionController tc,
                                long tableId,
                                long rowEstimate)
                         throws StandardException
        Sets the row estimate for the heap conglomerate.
        Parameters:
        tc - transaction to use
        tableId - the heap table
        rowEstimate - estimate of number of rows in the table
        Throws:
        StandardException - if accessing the table fails

      • run

        public void run()
        Drives the statistics generation.

        This method will be run in a separate thread, and it will keep working as long as there is work to do. When the queue is exhausted, the method will exit (the thread dies).

        Specified by:
        run in interface java.lang.Runnable

      • processingLoop

        private void processingLoop()
        Main processing loop which will compute statistics until the queue of scheduled work units has been drained.

      • stop

        public void stop()
        Stops the daemon.

        Will also clear the queue and print runtime statistics to the log the first time the method is invoked.

        Specified by:
        stop in interface IndexStatisticsDaemon

      • handleFatalErrors

        private boolean handleFatalErrors​(ContextManager cm,
                                  StandardException se)
        Handles fatal errors that will cause the daemon to be shut down.
        Parameters:
        cm - context manager
        se - the exception to handle
        Returns:
        true if the error was handled, false otherwise

      • handleExpectedErrors

        private boolean handleExpectedErrors​(TableDescriptor td,
                                     StandardException se)
        Handles expected errors.

        The logging of expected errors is for observability purposes only. The daemon is capable of dealing with these errors, and no interaction from the user is expected.

        Parameters:
        se - the exception to handle
        Returns:
        true if the error was handled, false otherwise

      • handleUnexpectedErrors

        private boolean handleUnexpectedErrors​(TableDescriptor td,
                                       StandardException se)
        Handles unexpected errors.

        Unexpected errors are error conditions the daemon isn't set up to handle specifically. For this reason the stack trace will be logged to allow for later investigation.

        In general it is expected that the daemon will be able to recover by dropping the current unit of work and move on to the next one (if any).

        Parameters:
        se - the exception to handle
        Returns:
        true if the error was handled, false otherwise

      • sleep

        private static void sleep​(long ms)
        Puts the current thread to sleep for maximum ms milliseconds.

        No guarantee is provided for the minimum amount of time slept. If interrupted, the interrupt flag will be set again.

        Parameters:
        ms - target sleep time

      • fmtScanTimes

        private static java.lang.String fmtScanTimes​(long[][] timings)
        Format array of scan durations as a string.

      • log

        private void log​(boolean asBackgroundTask,
                 TableDescriptor td,
                 java.lang.Throwable t,
                 java.lang.String msg)
        Logs the information given.

        Note that if asBackgroundTask is false, nothing will be logged currently.

        Parameters:
        asBackgroundTask - true if logging for the background daemon automatically updating stats, false if not
        td - current table descriptor being worked on, may be null
        t - raised error, may be null
        msg - the message to log

      • logAlways

        private void logAlways​(TableDescriptor td,
                       java.lang.Throwable t,
                       java.lang.String msg)
        Logs the information given.
        Parameters:
        td - current table descriptor being worked on, may be null
        t - raised error, may be null
        msg - the message to log

      • trace

        private void trace​(int indentLevel,
                   java.lang.String msg)

      • appendRunStats

        private void appendRunStats​(java.lang.StringBuffer sb)
        Appends runtime statistics to the given string buffer.
        Parameters:
        sb - the string buffer to append to

      • cardToStr

        private static java.lang.String cardToStr​(long[] cardinality)
        Produces a textual representation of the cardinality numbers.
        Parameters:
        cardinality - index cardinality
        Returns:
        A string.

      • extractIstatInfo

        private static java.lang.String extractIstatInfo​(java.lang.Throwable t)
        Purely for debugging, to avoid printing too much info.

      • getContextService

        private static ContextService getContextService()
        Privileged lookup of the ContextService. Must be private so that user code can't call this entry point.