Improve SQL Server Query Performance on Large Tables

Question

I have a relatively large table (currently 2 million records) and would like to know if it is possible to improve performance for special queries. Here is the ad-hoc keyword. Adding indexes is not an option (there are already indexes for the columns that are most often requested).

Running a simple query to return the 100 most recent updated records:

select top 100 * from ER101_ACCT_ORDER_DTL order by er101_upd_date_iso desc 

It takes a few minutes. See the implementation plan below:

Additional information from the table scan:

 SQL Server Execution Times: CPU time = 3945 ms, elapsed time = 148524 ms. 

The server is quite powerful (from the memory of 48 GB RAM, a 24-core processor) running on a sql server r2 x64 server.

Update

I found this code to create a table with 1,000,000 records. I thought I could run SELECT TOP 100 * FROM testEnvironment ORDER BY mailAddress DESC on several different servers to find out if the server had limited disk access speeds.

 WITH t1(N) AS (SELECT 1 UNION ALL SELECT 1), t2(N) AS (SELECT 1 FROM t1 x, t1 y), t3(N) AS (SELECT 1 FROM t2 x, t2 y), Tally(N) AS (SELECT TOP 98 ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) FROM t3 x, t3 y), Tally2(N) AS (SELECT TOP 5 ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) FROM t3 x, t3 y), Combinations(N) AS (SELECT DISTINCT LTRIM(RTRIM(RTRIM(SUBSTRING(poss,aN,2)) + SUBSTRING(vowels,bN,1))) FROM Tally a CROSS JOIN Tally2 b CROSS APPLY (SELECT 'BCDFGHJKLMNPRSTVWZ SCSKKNSNSPSTBLCLFLGLPLSLBRCRDRFRGRPRTRVRSHSMGHCHPHRHWHBWCWSWTW') d(poss) CROSS APPLY (SELECT 'AEIOU') e(vowels)) SELECT IDENTITY(INT,1,1) AS ID, aN + bN AS N INTO #testNames FROM Combinations a CROSS JOIN Combinations b; SELECT IDENTITY(INT,1,1) AS ID, firstName, secondName INTO #testNames2 FROM (SELECT firstName, secondName FROM (SELECT TOP 1000 --1000 * 1000 = 1,000,000 rows N AS firstName FROM #testNames ORDER BY NEWID()) a CROSS JOIN (SELECT TOP 1000 --1000 * 1000 = 1,000,000 rows N AS secondName FROM #testNames ORDER BY NEWID()) b) innerQ; SELECT firstName, secondName, firstName + '.' + secondName + '@fake.com' AS eMail, CAST((ABS(CHECKSUM(NEWID())) % 250) + 1 AS VARCHAR(3)) + ' ' AS mailAddress, (ABS(CHECKSUM(NEWID())) % 152100) + 1 AS jID, IDENTITY(INT,1,1) AS ID INTO #testNames3 FROM #testNames2 SELECT IDENTITY(INT,1,1) AS ID, firstName, secondName, eMail, mailAddress + bN + bN AS mailAddress INTO testEnvironment FROM #testNames3 a INNER JOIN #testNames b ON a.jID = b.ID; --CLEAN UP USELESS TABLES DROP TABLE #testNames; DROP TABLE #testNames2; DROP TABLE #testNames3; 

But on three test servers, the request was executed almost instantly. Can anyone explain this?

Update 2

Thank you for the comments - please continue them ... they made me try to change the primary key index from non-clustered to clustered with quite interesting (and unexpected?) Results.

nonclustered:

 SQL Server Execution Times: CPU time = 3634 ms, elapsed time = 154179 ms. 

Cluster:

 SQL Server Execution Times: CPU time = 2650 ms, elapsed time = 52177 ms. 

How is this possible? Without an index in the er101_upd_date_iso column, how can you use a clustered index scan?

Update 3

As requested is the create script table:

 CREATE TABLE [dbo].[ER101_ACCT_ORDER_DTL]( [ER101_ORG_CODE] [varchar](2) NOT NULL, [ER101_ORD_NBR] [int] NOT NULL, [ER101_ORD_LINE] [int] NOT NULL, [ER101_EVT_ID] [int] NULL, [ER101_FUNC_ID] [int] NULL, [ER101_STATUS_CDE] [varchar](2) NULL, [ER101_SETUP_ID] [varchar](8) NULL, [ER101_DEPT] [varchar](6) NULL, [ER101_ORD_TYPE] [varchar](2) NULL, [ER101_STATUS] [char](1) NULL, [ER101_PRT_STS] [char](1) NULL, [ER101_STS_AT_PRT] [char](1) NULL, [ER101_CHG_COMMENT] [varchar](255) NULL, [ER101_ENT_DATE_ISO] [datetime] NULL, [ER101_ENT_USER_ID] [varchar](10) NULL, [ER101_UPD_DATE_ISO] [datetime] NULL, [ER101_UPD_USER_ID] [varchar](10) NULL, [ER101_LIN_NBR] [int] NULL, [ER101_PHASE] [char](1) NULL, [ER101_RES_CLASS] [char](1) NULL, [ER101_NEW_RES_TYPE] [varchar](6) NULL, [ER101_RES_CODE] [varchar](12) NULL, [ER101_RES_QTY] [numeric](11, 2) NULL, [ER101_UNIT_CHRG] [numeric](13, 4) NULL, [ER101_UNIT_COST] [numeric](13, 4) NULL, [ER101_EXT_COST] [numeric](11, 2) NULL, [ER101_EXT_CHRG] [numeric](11, 2) NULL, [ER101_UOM] [varchar](3) NULL, [ER101_MIN_CHRG] [numeric](11, 2) NULL, [ER101_PER_UOM] [varchar](3) NULL, [ER101_MAX_CHRG] [numeric](11, 2) NULL, [ER101_BILLABLE] [char](1) NULL, [ER101_OVERRIDE_FLAG] [char](1) NULL, [ER101_RES_TEXT_YN] [char](1) NULL, [ER101_DB_CR_FLAG] [char](1) NULL, [ER101_INTERNAL] [char](1) NULL, [ER101_REF_FIELD] [varchar](255) NULL, [ER101_SERIAL_NBR] [varchar](50) NULL, [ER101_RES_PER_UNITS] [int] NULL, [ER101_SETUP_BILLABLE] [char](1) NULL, [ER101_START_DATE_ISO] [datetime] NULL, [ER101_END_DATE_ISO] [datetime] NULL, [ER101_START_TIME_ISO] [datetime] NULL, [ER101_END_TIME_ISO] [datetime] NULL, [ER101_COMPL_STS] [char](1) NULL, [ER101_CANCEL_DATE_ISO] [datetime] NULL, [ER101_BLOCK_CODE] [varchar](6) NULL, [ER101_PROP_CODE] [varchar](8) NULL, [ER101_RM_TYPE] [varchar](12) NULL, [ER101_WO_COMPL_DATE] [datetime] NULL, [ER101_WO_BATCH_ID] [varchar](10) NULL, [ER101_WO_SCHED_DATE_ISO] [datetime] NULL, [ER101_GL_REF_TRANS] [char](1) NULL, [ER101_GL_COS_TRANS] [char](1) NULL, [ER101_INVOICE_NBR] [int] NULL, [ER101_RES_CLOSED] [char](1) NULL, [ER101_LEAD_DAYS] [int] NULL, [ER101_LEAD_HHMM] [int] NULL, [ER101_STRIKE_DAYS] [int] NULL, [ER101_STRIKE_HHMM] [int] NULL, [ER101_LEAD_FLAG] [char](1) NULL, [ER101_STRIKE_FLAG] [char](1) NULL, [ER101_RANGE_FLAG] [char](1) NULL, [ER101_REQ_LEAD_STDATE] [datetime] NULL, [ER101_REQ_LEAD_ENDATE] [datetime] NULL, [ER101_REQ_STRK_STDATE] [datetime] NULL, [ER101_REQ_STRK_ENDATE] [datetime] NULL, [ER101_LEAD_STDATE] [datetime] NULL, [ER101_LEAD_ENDATE] [datetime] NULL, [ER101_STRK_STDATE] [datetime] NULL, [ER101_STRK_ENDATE] [datetime] NULL, [ER101_DEL_MARK] [char](1) NULL, [ER101_USER_FLD1_02X] [varchar](2) NULL, [ER101_USER_FLD1_04X] [varchar](4) NULL, [ER101_USER_FLD1_06X] [varchar](6) NULL, [ER101_USER_NBR_060P] [int] NULL, [ER101_USER_NBR_092P] [numeric](9, 2) NULL, [ER101_PR_LIST_DTL] [numeric](11, 2) NULL, [ER101_EXT_ACCT_CODE] [varchar](8) NULL, [ER101_AO_STS_1] [char](1) NULL, [ER101_PLAN_PHASE] [char](1) NULL, [ER101_PLAN_SEQ] [int] NULL, [ER101_ACT_PHASE] [char](1) NULL, [ER101_ACT_SEQ] [int] NULL, [ER101_REV_PHASE] [char](1) NULL, [ER101_REV_SEQ] [int] NULL, [ER101_FORE_PHASE] [char](1) NULL, [ER101_FORE_SEQ] [int] NULL, [ER101_EXTRA1_PHASE] [char](1) NULL, [ER101_EXTRA1_SEQ] [int] NULL, [ER101_EXTRA2_PHASE] [char](1) NULL, [ER101_EXTRA2_SEQ] [int] NULL, [ER101_SETUP_MSTR_SEQ] [int] NULL, [ER101_SETUP_ALTERED] [char](1) NULL, [ER101_RES_LOCKED] [char](1) NULL, [ER101_PRICE_LIST] [varchar](10) NULL, [ER101_SO_SEARCH] [varchar](9) NULL, [ER101_SSB_NBR] [int] NULL, [ER101_MIN_QTY] [numeric](11, 2) NULL, [ER101_MAX_QTY] [numeric](11, 2) NULL, [ER101_START_SIGN] [char](1) NULL, [ER101_END_SIGN] [char](1) NULL, [ER101_START_DAYS] [int] NULL, [ER101_END_DAYS] [int] NULL, [ER101_TEMPLATE] [char](1) NULL, [ER101_TIME_OFFSET] [char](1) NULL, [ER101_ASSIGN_CODE] [varchar](10) NULL, [ER101_FC_UNIT_CHRG] [numeric](13, 4) NULL, [ER101_FC_EXT_CHRG] [numeric](11, 2) NULL, [ER101_CURRENCY] [varchar](3) NULL, [ER101_FC_RATE] [numeric](12, 5) NULL, [ER101_FC_DATE] [datetime] NULL, [ER101_FC_MIN_CHRG] [numeric](11, 2) NULL, [ER101_FC_MAX_CHRG] [numeric](11, 2) NULL, [ER101_FC_FOREIGN] [numeric](12, 5) NULL, [ER101_STAT_ORD_NBR] [int] NULL, [ER101_STAT_ORD_LINE] [int] NULL, [ER101_DESC] [varchar](255) NULL ) ON [PRIMARY] SET ANSI_PADDING OFF ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_PRT_SEQ_1] [varchar](12) NULL SET ANSI_PADDING ON ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_PRT_SEQ_2] [varchar](120) NULL SET ANSI_PADDING OFF ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TAX_BASIS] [char](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_RES_CATEGORY] [char](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_DECIMALS] [char](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TAX_SEQ] [varchar](7) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_MANUAL] [char](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TR_LC_RATE] [numeric](12, 5) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TR_FC_RATE] [numeric](12, 5) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TR_PL_RATE] [numeric](12, 5) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TR_DIFF] [char](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TR_UNIT_CHRG] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TR_EXT_CHRG] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TR_MIN_CHRG] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TR_MAX_CHRG] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_PL_UNIT_CHRG] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_PL_EXT_CHRG] [numeric](13, 2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_PL_MIN_CHRG] [numeric](13, 2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_PL_MAX_CHRG] [numeric](13, 2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TAX_RATE_TYPE] [char](1) NULL SET ANSI_PADDING ON ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ORDER_FORM] [varchar](2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_FACTOR] [int] NULL SET ANSI_PADDING OFF ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_MGMT_RPT_CODE] [varchar](6) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ROUND_CHRG] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_WHOLE_QTY] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SET_QTY] [numeric](15, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SET_UNITS] [numeric](15, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SET_ROUNDING] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SET_SUB] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TIME_QTY] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_GL_DISTR_PCT] [numeric](7, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_REG_SEQ] [int] NULL SET ANSI_PADDING ON ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ALT_DESC] [varchar](255) NULL SET ANSI_PADDING OFF ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_REG_ACCT] [varchar](8) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_DAILY] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_AVG_UNIT_CHRG] [varchar](1) NULL SET ANSI_PADDING ON ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ALT_DESC2] [varchar](255) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_CONTRACT_SEQ] [int] NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ORIG_RATE] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_DISC_PCT] [decimal](17, 10) NULL SET ANSI_PADDING OFF ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_DTL_EXIST] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ORDERED_ONLY] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SHOW_STDATE] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SHOW_STTIME] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SHOW_ENDATE] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SHOW_ENTIME] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SHOW_RATE] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SHOW_UNITS] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_BASE_RATE] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_COMMIT_QTY] [numeric](11, 2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_MM_QTY_USED] [varchar](2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_MM_CHRG_USED] [varchar](2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ITEM_TEXT_1] [varchar](50) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ITEM_NBR_1] [numeric](13, 3) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ITEM_NBR_2] [numeric](13, 3) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ITEM_NBR_3] [numeric](13, 3) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_PL_BASE_RATE] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_REV_DIST] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_COVER] [int] NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_RATE_TYPE] [varchar](2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_USE_SEASONAL] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TAX_EI] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TAXES] [numeric](13, 2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_FC_TAXES] [numeric](13, 2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_PL_TAXES] [numeric](13, 2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_FC_QTY] [numeric](13, 2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_LEAD_HRS] [numeric](6, 2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_STRIKE_HRS] [numeric](6, 2) NULL SET ANSI_PADDING ON ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_CANCEL_USER_ID] [varchar](10) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ST_OFFSET_HRS] [numeric](7, 2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_EN_OFFSET_HRS] [numeric](7, 2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_MEMO_FLAG] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_MEMO_EXT_CHRG] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_MEMO_EXT_CHRG_PL] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_MEMO_EXT_CHRG_TR] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_MEMO_EXT_CHRG_FC] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TIME_QTY_EDIT] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SURCHARGE_PCT] [decimal](17, 10) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_INCL_EXT_CHRG] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_INCL_EXT_CHRG_FC] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_CARRIER] [varchar](6) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SETUP_ID2] [varchar](8) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SHIPPABLE] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_CHARGEABLE] [varchar](2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ITEM_NBR_ALLOW] [varchar](2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ITEM_NBR_START] [int] NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ITEM_NBR_END] [int] NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ITEM_SUPPLIER] [varchar](8) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_TRACK_ID] [varchar](40) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_REF_INV_NBR] [int] NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_NEW_ITEM_STS] [varchar](2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_MSTR_REG_ACCT_CODE] [varchar](8) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ALT_DESC3] [varchar](255) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ALT_DESC4] [varchar](255) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ALT_DESC5] [varchar](255) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SETUP_ROLLUP] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_MM_COST_USED] [varchar](2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_AUTO_SHIP_RCD] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ITEM_FIXED] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ITEM_EST_TBD] [varchar](3) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ROLLUP_PL_UNIT_CHRG] [numeric](13, 4) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ROLLUP_PL_EXT_CHRG] [numeric](13, 2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_GL_ORD_REV_TRANS] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_DISCOUNT_FLAG] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SETUP_RES_TYPE] [varchar](6) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SETUP_RES_CODE] [varchar](12) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_PERS_SCHED_FLAG] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_PRINT_STAMP] [datetime] NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SHOW_EXT_CHRG] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_PRINT_SEQ_NBR] [int] NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_PAY_LOCATION] [varchar](3) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_MAX_RM_NIGHTS] [int] NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_USE_TIER_COST] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_UNITS_SCHEME_CODE] [varchar](6) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_ROUND_TIME] [varchar](2) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_LEVEL] [int] NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_SETUP_PARENT_ORD_LINE] [int] NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_BADGE_PRT_STS] [varchar](1) NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_EVT_PROMO_SEQ] [int] NULL ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD [ER101_REG_TYPE] [varchar](12) NULL /****** Object: Index [PK__ER101_ACCT_ORDER] Script Date: 04/15/2012 20:24:37 ******/ ALTER TABLE [dbo].[ER101_ACCT_ORDER_DTL] ADD CONSTRAINT [PK__ER101_ACCT_ORDER] PRIMARY KEY CLUSTERED ( [ER101_ORD_NBR] ASC, [ER101_ORD_LINE] ASC, [ER101_ORG_CODE] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 50) ON [PRIMARY] 

The table is 2.8 GB in size with an index of 3.9 GB.

Answer 1

There are several problems with this request (and this applies to each request).

Lack of index

The lack of index in the er101_upd_date_iso column er101_upd_date_iso most important since Oded has already been mentioned.

Without an index match (which cannot cause a table scan), there is no way to run quick queries on large tables.

If you cannot add indexes (for various reasons, including it makes no sense to create an index for only one special query), I would suggest several workarounds (which can be used for special queries):

1. Use temporary tables

Create a temporary table in the subset (rows and columns) of the data you are interested in. The temporary table should be much smaller than the original source table, can be easily indexed (if necessary), and can cache a subset of the data that interests you.

To create a temporary table, you can use code (not verified), for example:

 -- copy records from last month to temporary table INSERT INTO #my_temporary_table SELECT * FROM er101_acct_order_dtl WITH (NOLOCK) WHERE er101_upd_date_iso > DATEADD(month, -1, GETDATE()) -- you can add any index you need on temp table CREATE INDEX idx_er101_upd_date_iso ON #my_temporary_table(er101_upd_date_iso) -- run other queries on temporary table (which can be indexed) SELECT TOP 100 * FROM #my_temporary_table ORDER BY er101_upd_date_iso DESC 

Pros:

• Easy to make for any subset of data.
• Ease of management is temporary and this table.
• Does not affect the overall system performance, for example view .
• A temporary table can be indexed.
• You do not need to worry about this - this is temporary :).

Minuses:

• This is a snapshot of the data - but it is probably good enough for most special queries.

2. General table expression - CTE

Personally, I often use CTE with special requests - it helps a lot in building (and testing) the request in parts.

See the example below (query starting with WITH ).

Pros:

• It’s easy to create, starting from a large view, and then selecting and filter what you really need.
• Easy to check.

Minuses:

• Some people don't like CDE queries - CDE seems to be long and hard to understand.

3. Create views

Similarly above, but create views instead of temporary tables (if you often play with the same queries, and you have a version of MS SQL that supports indexed views.

You can create views or indexed views on a subset of the data that interests you and run view queries — which should only contain an interesting subset of data, much smaller than the entire table.

Pros:

• Easy to do.
• It is updated with the original data.

Minuses:

• Only possible for a specific subset of data.
• May be ineffective for large tables with high refresh rates.
• It’s not easy to manage.
• May affect overall system performance.
• I am not sure that indexed views are available in every version of MS SQL.

Select All Columns

Running a query on a star ( SELECT * FROM ) on a large table is not very good ...

If you have large columns (for example, long rows), it takes a lot of time to read them from disk and transfer them over the network.

I would try to replace * with the column names that you really need.

Or, if you need all the columns, try rewriting the query with something like (using a common data expression):

 ;WITH recs AS ( SELECT TOP 100 id as rec_id -- select primary key only FROM er101_acct_order_dtl ORDER BY er101_upd_date_iso DESC ) SELECT er101_acct_order_dtl.* FROM recs JOIN er101_acct_order_dtl ON er101_acct_order_dtl.id = recs.rec_id ORDER BY er101_upd_date_iso DESC 

Dirty read

The last thing, which can speed up the ad-hoc query, allows dirty readings with the prompt of the WITH (NOLOCK) table .

Instead of a hint, you can set the transaction isolation level for reading without specifying:

 SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED 

or set the correct configuration of SQL Management Studio.

I assume dirty reads are good enough for ad-hoc requests.

Answer 2

The simple answer is NO. You cannot help ad hoc queries in a 238 column table with a 50% fill factor in a clustered index.

Detailed answer:

As I said in other answers to this topic, index design is both art and science, and there are so many factors that believe that there are several, if any, hard and fast rules. You should consider: the volume of DML operations against SELECT, the disk subsystem, other indexes / triggers in the table, the distribution of data inside the table are queries using SARGable WHERE conditions and several other things that I can’t even remember Now.

I can say that no help can be provided for questions on this topic without understanding the table itself, its indexes, triggers, etc. Now that you have placed the table definition (still waiting for indexes, but the table definition alone indicates 99% of the problem). I can offer some suggestions.

Firstly, if the exact definition of the table (238 columns, 50% Fill Factor), you can largely ignore the rest of the answers / recommendations here ;-). Sorry that here is less than political, but seriously, this is a wild hunt for geese, not knowing the specifics. And now, when we see the definition of the table, it becomes a little clearer why a simple query takes a lot of time, even when test queries (Update # 1) run so fast.

The main problem here (and in many situations with low efficiency) is poor data modeling. 238 columns are not prohibited, since 999 indexes are not prohibited, but this is also not very reasonable.

Recommendations:

• Firstly, this table really needs reconstruction. If this is a data warehouse table, then it is possible, but if not, then these fields should really be divided into several tables that can have the same PK. You will have a master record table, and the child tables will only have dependent information based on generally accepted attributes, and the PK of these tables is the same as the PK of the main table and therefore the FK in the main table. There will be a 1 to 1 relationship between the main and all child tables.
• Using ANSI_PADDING OFF is a concern, not to mention inconsistencies within the table due to various additions of columns over time. Not sure if you can fix this now, but ideally you will always have ANSI_PADDING ON or at least have the same settings for all ALTER TABLE statements.
• Consider creating two additional file groups: tables and indexes. It’s better not to put your stuff in PRIMARY , as SQL SERVER stores all its data and metadata about your objects. You create a table and a clustered index (like data for a table) on [Tables] and all indices without clustering on [Indexes]
• Increase fill factor from 50%. This is a small number, probably why your index space is larger than your data space. Performing an index rebuild recreates data pages with a maximum size of 4k (out of a total page size of 8k) used for your data so that your table is spread across a wide area.
• If most or all of the queries have the condition "ER101_ORG_CODE" in WHERE , consider moving it to the leading column of the clustered index. Assuming it is used more often than "ER101_ORD_NBR". If "ER101_ORD_NBR" is used more often, then save it. , , "OrganizationCode" "OrderNumber", "OrgCode" - , "OrderNumbers".
• , "ER101_ORG_CODE" 2 , CHAR(2) VARCHAR(2) , , .
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Good luck

UPDATE
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UPDATE 2
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Answer 3

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Answer 6

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Answer 7

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 -- From Glen Barry -- Clear Wait Stats (consider clearing and running wait stats query again after a few minutes) -- DBCC SQLPERF('sys.dm_os_wait_stats', CLEAR); -- Check Task Counts to get an initial idea what the problem might be -- Avg Current Tasks Count, Avg Runnable Tasks Count, Avg Pending Disk IO Count across all schedulers -- Run several times in quick succession SELECT AVG(current_tasks_count) AS [Avg Task Count], AVG(runnable_tasks_count) AS [Avg Runnable Task Count], AVG(pending_disk_io_count) AS [Avg Pending DiskIO Count] FROM sys.dm_os_schedulers WITH (NOLOCK) WHERE scheduler_id < 255 OPTION (RECOMPILE); -- Sustained values above 10 suggest further investigation in that area -- High current_tasks_count is often an indication of locking/blocking problems -- High runnable_tasks_count is a good indication of CPU pressure -- High pending_disk_io_count is an indication of I/O pressure 

Answer 8

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Answer 9

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