how to clean huge Dbwarden QueryHistory table
This script will help: http://www.sqlservercentral.com/scripts/dbWarden+monitoring+maintenance/118935/

As per description, "This script creates/modifies all objects necessary for a cleanup of dbWarden History."

Note it is behind a login to SQLServerCentral.Com but if you are using dbWarden I expect you have a login to that site already.

Below is the script (just incase if SCC is down or the article gets removed):

-- Ref: http://www.sqlservercentral.com/scripts/dbWarden+monitoring+maintenance/118935/
IF  NOT EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[Proc4HistoryTableCleanup]'))
BEGIN
    EXECUTE ('CREATE PROCEDURE [dbo].[Proc4HistoryTableCleanup] ( ' +
            '    @TableOwner    varchar(64),' +
            '    @TableName     varchar(512), ' +
            '    @DateFieldName varchar(50), ' +
            '    @retentionDays INT = 0,' +
            '    @Debug         TINYINT = 0' +
            ') ' +
            'AS ' +
            'BEGIN ' +
            '   SELECT ''Not implemented'' ' +
            'END')  
END
GO

ALTER PROCEDURE [dbo].[Proc4HistoryTableCleanup] (
    @TableOwner     varchar(64),
    @TableName      varchar(64),
    @DateFieldName  varchar(64),
    @retentionDays  INT,
    @maxRowCnt      INT = 10000,
    @debug          TINYINT = 0
)
AS
/*
 ===================================================================================
  DESCRIPTION:
    This procedure takes in charge the clean-up for a given table based on a date field
    given as parameter and a retention expressed as a number of days.
    If the number of records to delete is more than a configurable limit, a dichotomic 
    delete will be performed so that there is no matter on big open transaction without 
    commit.

  ARGUMENTS :
    @TableOwner     name of the owner of the table to clean up
    @TableName      name of the table to clean up
    @DateFieldName  name of the date field to use for clean up
    @retentionDays  number of days to keep track
    @maxRowCnt      maximal number of rows to consider in an open transaction.
                    If the cleanup needs more than that number, the query will be cut 
                    into pieces implying maximum @maxRowCnt
    @debug          if set to 1, this enables the debug mode

  REQUIREMENTS:

  ==================================================================================
  BUGS:

    BUGID       Fixed   Description
    ==========  =====   ==========================================================  
    ----------------------------------------------------------------------------------
  ==================================================================================
  NOTES:
  AUTHORS:
       .   VBO     Vincent Bouquette   (vincent.bouquette@chu.ulg.ac.be)
       .   BBO     Bernard Bozert      (bernard.bozet@chu.ulg.ac.be)
       .   JEL     Jefferson Elias     (jelias@chu.ulg.ac.be)

  COMPANY: CHU Liege
  ==================================================================================
  Revision History

    Date        Nom         Description
    ==========  =====       ==========================================================
    18/11/2014  JEL         Version 0.1.0
    ----------------------------------------------------------------------------------
 ===================================================================================
*/

BEGIN

    --SET NOCOUNT ON;

    DECLARE @versionNb        varchar(16) = '0.1.0';
    DECLARE @tsql             nvarchar(max);            -- text to execute via dynamic SQL
    DECLARE @tmpRetentionDays INT;                      -- number of retention days to remove 
    DECLARE @retentionInc     INT;                      -- increment for tmpRetentionDays


    BEGIN TRY
        -- 
        -- check parameter :
        --      retention days 
        --
        if @retentionDays &lt; 0
        BEGIN
            RAISERROR ('Parameter "retentionDays" is negative. Avorting execution', 10,1,@retentionDays);
        END     

        if @retentionDays = 0
            return

        --
        -- check parameters
        --      table-related parameters are usable ?
        --
        IF(NOT EXISTS (
            SELECT 1
            FROM 
                information_schema.COLUMNS 
            where 
                TABLE_CATALOG= DB_NAME(DB_id()) -- in current database
            AND TABLE_SCHEMA = @TableOwner
            AND TABLE_NAME   = @TableName
            and COLUMN_NAME  = @DateFieldName
          ))

        BEGIN           
            RAISERROR('Parameters about the table are unusable in current database ', 10,1,@TableOwner, @TableName ,@DateFieldName )
        END

        if @debug = 1
        BEGIN
            PRINT '----------------------------------------------------'
            PRINT OBJECT_NAME(@@PROCID)
            PRINT '===================================================='
            PRINT 'Owner      = ' + @TableOwner
            PRINT 'TableName  = ' + @TableName
            PRINT 'Column     = ' + @DateFieldName
            PRINT 'Retention  = ' + CONVERT (VARCHAR ,@retentionDays)
            PRINT 'Max Row Nb = ' + CONVERT (VARCHAR ,@maxRowCnt)
            PRINT '----------------------------------------------------'
            PRINT CHAR(10)
        END

        -- 
        -- Iteration number evaluation
        --
        DECLARE @dateThresh DATETIME
        SET @dateThresh = GETDATE() - @retentionDays

        DECLARE @dateThreshStr   VARCHAR(100)
        SELECT @dateThreshStr = convert(varchar(100),@dateThresh,112)

        DECLARE @totalRecordNb   BIGINT
        DECLARE @MinDateFieldVal DATETIME

        SET @tsql =  N'SELECT '                             + CHAR(10) +
                    '    @totalRecNb = COUNT_BIG(*),'               + CHAR(10) +
                    '    @minDate    = MIN([' + @DateFieldName + '])'   + CHAR(10) +
                    'FROM'  + CHAR(10) +
                    '    [' + @TableOwner + '].[' + @TableName + ']' + CHAR(10) +
                    'WHERE' + CHAR(10) +
                    '    '  + @DateFieldName + ' &lt; convert(DATETIME,@dateThresh,112)'

        execute sp_executesql @tsql, N'@totalRecNb BIGINT OUTPUT, @minDate DATETIME OUTPUT,@dateThresh VARCHAR(100)', @minDate = @MinDateFieldVal OUTPUT, @totalRecNb = @totalRecordNb OUTPUT, @dateThresh = @dateThreshStr

        if @debug = 1
        BEGIN
            PRINT 'Min Date in table : ' + CONVERT (VARCHAR ,@MinDateFieldVal,112)
            PRINT 'Number of records : ' + CONVERT (VARCHAR ,@totalRecordNb)
        END

        if(@totalRecordNb &gt; @maxRowCnt) 
        BEGIN               

            -- divide by 2 the number of days between min date and the retention period
            DECLARE @nbOfDaysToAdd INT
            SELECT @nbOfDaysToAdd = (DATEDIFF(day,@MinDateFieldVal,@dateThresh) / 2)

            if @debug = 1
            BEGIN
                PRINT 'Too many records to take care at once !'
                PRINT 'Days to play with : ' + CONVERT (VARCHAR ,@nbOfDaysToAdd)
            END 

            -- TODO : if days is not enough =&gt; play with hours !        

            SET @tmpRetentionDays = @retentionDays+@nbOfDaysToAdd
            if @debug = 1
            BEGIN               
                PRINT 'New retention : ' + convert(varchar,@tmpRetentionDays)
            END     

            exec [dbo].[Proc4HistoryTableCleanup] @TableOwner=@TableOwner,@TableName=@TableName,@DateFieldName=@DateFieldName,@retentionDays=@tmpRetentionDays,@maxRowCnt=@maxRowCnt,@debug=@debug          

            if @debug = 1
            BEGIN
                PRINT 'Restarting procedure with the previous retention :' + CONVERT (varchar,@retentionDays)
            END

            execute [dbo].[Proc4HistoryTableCleanup] @TableOwner=@TableOwner,@TableName=@TableName,@DateFieldName=@DateFieldName,@retentionDays=@retentionDays,@maxRowCnt=@maxRowCnt,@debug=@debug
        END
        ELSE
        BEGIN           
            if @debug = 1
            BEGIN
                PRINT 'Deleting ' + CONVERT (varchar,@totalRecordNb) + ' records' 
            END

            SET @tsql = 'DELETE'    + CHAR(10) +
                        'FROM'  + CHAR(10) +
                        '    [' + @TableOwner + '].[' + @TableName + ']' + CHAR(10) +
                        'WHERE' + CHAR(10) +
                        '    '  + @DateFieldName + ' &lt; convert(DATETIME,@dateThresh,112)'

            execute sp_executesql @tsql, N'@dateThresh VARCHAR(100)', @dateThresh = @dateThreshStr                      

            if @debug = 1
            BEGIN
                SET @tsql =  N'SELECT '                             + CHAR(10) +
                        '    @totalRecNb = COUNT_BIG(*),'               + CHAR(10) +
                        '    @minDate    = MIN([' + @DateFieldName + '])'   + CHAR(10) +
                        'FROM'  + CHAR(10) +
                        '    [' + @TableOwner + '].[' + @TableName + ']' + CHAR(10) +
                        'WHERE' + CHAR(10) +
                        '    '  + @DateFieldName + ' &lt; convert(DATETIME,@dateThresh,112)'

                execute sp_executesql @tsql, N'@totalRecNb BIGINT OUTPUT, @minDate DATETIME OUTPUT,@dateThresh VARCHAR(100)', @minDate = @MinDateFieldVal OUTPUT, @totalRecNb = @totalRecordNb OUTPUT, @dateThresh = @dateThreshStr         

                PRINT 'Nb of records after delete : ' + CONVERT (varchar,@totalRecordNb)
                PRINT 'Minimum date after delete  : ' + CONVERT(varchar,@MinDateFieldVal,112)
            END             

        END


    END TRY

    BEGIN CATCH
        PRINT 'ErrorNumber    : ' + CONVERT (VARCHAR , ERROR_NUMBER())
        PRINT 'ErrorSeverity  : ' + CONVERT (VARCHAR , ERROR_SEVERITY())
        PRINT 'ErrorState     : ' + CONVERT (VARCHAR , ERROR_STATE())
        PRINT 'ErrorProcedure : ' + CONVERT (VARCHAR , ERROR_PROCEDURE())
        PRINT 'ErrorLine      : ' + CONVERT (VARCHAR , ERROR_LINE())
        PRINT 'ErrorMessage   : ' + CONVERT (VARCHAR , ERROR_MESSAGE()) 
        IF @@TRANCOUNT &gt; 0
            ROLLBACK TRAN --RollBack in case of Error

        RAISERROR ('Unable to proceed !', 10,1,@retentionDays);

    END CATCH
END 

/**

Usage example :
==============
exec dbo.Proc4HistoryTableCleanup 
    @TableOwner     = 'dbo',
    @TableName      = 'CPUStatsHistory',
    @DateFieldName  = 'DateStamp',
    @retentionDays  = 700,
    @debug          = 1

exec dbo.Proc4HistoryTableCleanup 
    @TableOwner     = 'dbo',
    @TableName      = 'CPUStatsHistory',
    @DateFieldName  = 'DateStamp',
    @retentionDays  = 300,
    @debug          = 1     
*/


alter table  dbo.DataDictionary_Tables 
add retentionDays INT DEFAULT 90

update dbo.DataDictionary_Tables
set retentionDays = null
where TableName in (
    'AlertContacts','AlertSettings','DatabaseSettings','DataDictionary_Fields',
    'DataDictionary_Tables','SchemaChangeLog','ServerChangeLog'
)

update dbo.DataDictionary_Tables
set retentionDays = 90
where TableName in (
    'BlockingHistory','CPUStatsHistory','FileStatsHistory','HealthReport','JobStatsHistory',
    'MemoryUsageHistory','PerfStatsHistory','QueryHistory'
)

alter table  dbo.DataDictionary_Tables 
add dateField VARCHAR(100)

update dbo.DataDictionary_Tables
set dateField = 'DateStamp'
where TableName in (
    'BlockingHistory','CPUStatsHistory','HealthReport',
    'MemoryUsageHistory','QueryHistory'
)
update dbo.DataDictionary_Tables
set dateField = 'FileStatsDateStamp'
where TableName = 'FileStatsHistory'

update dbo.DataDictionary_Tables
set dateField = 'JobStatsDateStamp'
where TableName = 'JobStatsHistory'

update dbo.DataDictionary_Tables
set dateField = 'StatDate'
where TableName = 'PerfStatsHistory'


create view dbo.CleanupSettings
AS
select 
    SchemaName,
    TableName,
    dateField as DateFieldName,
    retentionDays
from dbo.DataDictionary_Tables 
where retentionDays is not null;


IF  NOT EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[dbWarden_HistoryCleanup]'))
BEGIN
    EXECUTE ('CREATE PROCEDURE [dbo].[dbWarden_HistoryCleanup] ( ' +            
            '    @Debug         TINYINT = 0' +
            ') ' +
            'AS ' +
            'BEGIN ' +
            '   SELECT ''Not implemented'' ' +
            'END')  
END
GO

ALTER PROCEDURE [dbo].dbWarden_HistoryCleanup ( 
    @debug          TINYINT = 0
)
AS
/*
 ===================================================================================
  DESCRIPTION:
    This procedure takes care of purging old data inside tables defined in the
    table or view dbo.CleanupSettings of the same database as the one in which this
    procedure has been created.

  ARGUMENTS :
    @debug          if set to 1, this enables the debug mode

  REQUIREMENTS:

  ==================================================================================
  BUGS:

    BUGID       Fixed   Description
    ==========  =====   ==========================================================  
    ----------------------------------------------------------------------------------
  ==================================================================================
  NOTES:
  AUTHORS:
       .   VBO     Vincent Bouquette   (vincent.bouquette@chu.ulg.ac.be)
       .   BBO     Bernard Bozert      (bernard.bozet@chu.ulg.ac.be)
       .   JEL     Jefferson Elias     (jelias@chu.ulg.ac.be)

  COMPANY: CHU Liege
  ==================================================================================
  Revision History

    Date        Nom         Description
    ==========  =====       ==========================================================
    19/11/2014  JEL         Version 0.1.0
    ----------------------------------------------------------------------------------
 ===================================================================================
*/

BEGIN

    --SET NOCOUNT ON;

    DECLARE @versionNb        varchar(16) = '0.1.0';
    DECLARE @tsql             nvarchar(max);            -- text to execute via dynamic SQL

    DECLARE @CurrentOwner       VARCHAR(50)
    DECLARE @CurrentTable       VARCHAR(50)
    DECLARE @CurrentColumn      VARCHAR(50)
    DECLARE @CurrentRetention   INT

    DECLARE getTablesToPurge CURSOR FOR
        SELECT *
        FROM [dbo].[CleanupSettings]                

    open getTablesToPurge
    FETCH NEXT
    FROM getTablesToPurge INTO @CurrentOwner,@CurrentTable,@CurrentColumn,@CurrentRetention

    WHILE @@FETCH_STATUS = 0
    BEGIN

        if @debug = 1 
        BEGIN
            PRINT 'Current Owner  : '    + @CurrentOwner
            PRINT 'Current Table  : '    + @CurrentTable
            PRINT 'Current Column : '    + @CurrentColumn + '(datetime column used in where clause)'
            PRINT 'Current retention : ' + convert(varchar,@CurrentRetention)
        END

        exec dbo.Proc4HistoryTableCleanup 
            @TableOwner     = @CurrentOwner,
            @TableName      = @CurrentTable,
            @DateFieldName  = @CurrentColumn,
            @retentionDays  = @CurrentRetention,
            @debug          = @debug

        -- carry on ...
        FETCH NEXT
        FROM getTablesToPurge INTO @CurrentOwner,@CurrentTable,@CurrentColumn,@CurrentRetention
    END
    CLOSE getTablesToPurge
    DEALLOCATE getTablesToPurge

END


/**

Usage example :
==============
exec dbo.[dbWarden_HistoryCleanup] 
    @debug          = 1

exec dbo.[dbWarden_HistoryCleanup]
*/


-- 
-- ------------------------------
-- Sample job : everyday @8:15PM
-- ------------------------------
--
IF NOT EXISTS (SELECT * FROM msdb..sysjobs WHERE name = 'dbWarden_HistoryCleanup')
BEGIN
    BEGIN TRANSACTION
        DECLARE @ReturnCode INT
        SELECT @ReturnCode = 0

        DECLARE @jobId BINARY(16)
        EXEC 
            @ReturnCode =  msdb..sp_add_job @job_name=N'dbWarden_HistoryCleanup', 
            @enabled=1, 
            @notify_level_eventlog=0, 
            @notify_level_email=2, 
            @notify_level_netsend=0, 
            @notify_level_page=0, 
            @delete_level=0, 
            @description=N'No description available.', 
            @category_name=N'Database Monitoring', 
            @owner_login_name=N'sa', 
            @notify_email_operator_name=N'SQL_DBA', @job_id = @jobId OUTPUT

        IF (@@ERROR &lt;&gt; 0 OR @ReturnCode &lt;&gt; 0) GOTO QuitWithRollback

        EXEC 
            @ReturnCode = msdb..sp_add_jobstep @job_id=@jobId, @step_name=N'run proc', 
            @step_id=1, 
            @cmdexec_success_code=0, 
            @on_success_action=1, 
            @on_success_step_id=0, 
            @on_fail_action=2, 
            @on_fail_step_id=0, 
            @retry_attempts=0, 
            @retry_interval=0, 
            @os_run_priority=0, @subsystem=N'TSQL', 
            @command=N'SET NOCOUNT ON
EXEC [DBA].dbo.dbWarden_HistoryCleanup', 
            @database_name=N'master', 
            @flags=0

        IF (@@ERROR &lt;&gt; 0 OR @ReturnCode &lt;&gt; 0) GOTO QuitWithRollback

        EXEC @ReturnCode = msdb..sp_update_job @job_id = @jobId, @start_step_id = 1

        DECLARE @schedule_id int
        EXEC msdb.dbo.sp_add_jobschedule    @job_id=@jobId, @name=N'dbWarden_Schedule_HistoryCleanup', 
                                            @enabled=1, 
                                            @freq_type=4, 
                                            @freq_interval=1, 
                                            @freq_subday_type=1, 
                                            @freq_subday_interval=0, 
                                            @freq_relative_interval=0, 
                                            @freq_recurrence_factor=1, 
                                            @active_start_date=20141119, 
                                            @active_end_date=99991231, 
                                            @active_start_time=201500, 
                                            @active_end_time=235959, @schedule_id = @schedule_id OUTPUT

        IF (@@ERROR &lt;&gt; 0 OR @ReturnCode &lt;&gt; 0) GOTO QuitWithRollback

        EXEC @ReturnCode = msdb..sp_add_jobserver @job_id = @jobId, @server_name = N'(local)'
        IF (@@ERROR &lt;&gt; 0 OR @ReturnCode &lt;&gt; 0) GOTO QuitWithRollback

        COMMIT TRANSACTION
        GOTO EndSave
QuitWithRollback:
        IF (@@TRANCOUNT &gt; 0) ROLLBACK TRANSACTION
EndSave:
END
GO