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  • Fix: Connections to SQL Server 2005 on Windows Vista suddenly stop working

    - by NTulip
    On my Vista machine at work, applications and the SQL Server Management Console work fine connecting to SQL Server 2005. Sometimes they are ok for weeks at a time, sometime for hours and then they stop connecting. I've tried everything to get it to work including the installation of SPII and running the user provisioning tool without any luck. The only way to fix it was to restart. The Error: Connections are refused with the standard error message: Cannot connect to SERVER_NAME\INSTANCE_NAME ------------------------------ ADDITIONAL INFORMATION: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified) (Microsoft SQL Server, Error: -1) For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&EvtSrc=MSSQLServer&EvtID=-1&LinkId=20476 The Fix: Stop and restart the Sql Server Browser, Sql Server integration, SQL Server Active Directory Helper services. Works like a charm.

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  • Advice needed: warm backup solution for SQL Server 2008 Express?

    - by Mikey Cee
    What are my options for achieving a warm backup server for a SQL Server Express instance running a single database? Sitting beside my production SQL Server 2008 Express box I have a second physical box currently doing nothing. I want to use this second box as a warm backup server by somehow replicating my production database in near real time (a little bit of data loss is acceptable). The database is very small and resources are utilized very lightly. In the case that the production server dies, I would manually reconfigure my application to point to the backup server instead. Although Express doesn't support log shipping natively, I am thinking that I could manually script a poor man's version of it, where I use batch files to take the logs and copy them across the network and apply them to the second server at 5 minute intervals. Does anyone have any advice on whether this is technically achievable, or if there is a better way to do what I am trying to do? Note that I want to avoid having to pay for the full version of SQL Server and configure mirroring as I think it is an overkill for this application. I understand that other DB platforms may present suitable options (eg. a MySQL Cluster), but for the purposes of this discussion, let's assume we have to stick to SQL Server.

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  • Advanced TSQL Tuning: Why Internals Knowledge Matters

    - by Paul White
    There is much more to query tuning than reducing logical reads and adding covering nonclustered indexes.  Query tuning is not complete as soon as the query returns results quickly in the development or test environments.  In production, your query will compete for memory, CPU, locks, I/O and other resources on the server.  Today’s entry looks at some tuning considerations that are often overlooked, and shows how deep internals knowledge can help you write better TSQL. As always, we’ll need some example data.  In fact, we are going to use three tables today, each of which is structured like this: Each table has 50,000 rows made up of an INTEGER id column and a padding column containing 3,999 characters in every row.  The only difference between the three tables is in the type of the padding column: the first table uses CHAR(3999), the second uses VARCHAR(MAX), and the third uses the deprecated TEXT type.  A script to create a database with the three tables and load the sample data follows: USE master; GO IF DB_ID('SortTest') IS NOT NULL DROP DATABASE SortTest; GO CREATE DATABASE SortTest COLLATE LATIN1_GENERAL_BIN; GO ALTER DATABASE SortTest MODIFY FILE ( NAME = 'SortTest', SIZE = 3GB, MAXSIZE = 3GB ); GO ALTER DATABASE SortTest MODIFY FILE ( NAME = 'SortTest_log', SIZE = 256MB, MAXSIZE = 1GB, FILEGROWTH = 128MB ); GO ALTER DATABASE SortTest SET ALLOW_SNAPSHOT_ISOLATION OFF ; ALTER DATABASE SortTest SET AUTO_CLOSE OFF ; ALTER DATABASE SortTest SET AUTO_CREATE_STATISTICS ON ; ALTER DATABASE SortTest SET AUTO_SHRINK OFF ; ALTER DATABASE SortTest SET AUTO_UPDATE_STATISTICS ON ; ALTER DATABASE SortTest SET AUTO_UPDATE_STATISTICS_ASYNC ON ; ALTER DATABASE SortTest SET PARAMETERIZATION SIMPLE ; ALTER DATABASE SortTest SET READ_COMMITTED_SNAPSHOT OFF ; ALTER DATABASE SortTest SET MULTI_USER ; ALTER DATABASE SortTest SET RECOVERY SIMPLE ; USE SortTest; GO CREATE TABLE dbo.TestCHAR ( id INTEGER IDENTITY (1,1) NOT NULL, padding CHAR(3999) NOT NULL,   CONSTRAINT [PK dbo.TestCHAR (id)] PRIMARY KEY CLUSTERED (id), ) ; CREATE TABLE dbo.TestMAX ( id INTEGER IDENTITY (1,1) NOT NULL, padding VARCHAR(MAX) NOT NULL,   CONSTRAINT [PK dbo.TestMAX (id)] PRIMARY KEY CLUSTERED (id), ) ; CREATE TABLE dbo.TestTEXT ( id INTEGER IDENTITY (1,1) NOT NULL, padding TEXT NOT NULL,   CONSTRAINT [PK dbo.TestTEXT (id)] PRIMARY KEY CLUSTERED (id), ) ; -- ============= -- Load TestCHAR (about 3s) -- ============= INSERT INTO dbo.TestCHAR WITH (TABLOCKX) ( padding ) SELECT padding = REPLICATE(CHAR(65 + (Data.n % 26)), 3999) FROM ( SELECT TOP (50000) n = ROW_NUMBER() OVER (ORDER BY (SELECT 0)) - 1 FROM master.sys.columns C1, master.sys.columns C2, master.sys.columns C3 ORDER BY n ASC ) AS Data ORDER BY Data.n ASC ; -- ============ -- Load TestMAX (about 3s) -- ============ INSERT INTO dbo.TestMAX WITH (TABLOCKX) ( padding ) SELECT CONVERT(VARCHAR(MAX), padding) FROM dbo.TestCHAR ORDER BY id ; -- ============= -- Load TestTEXT (about 5s) -- ============= INSERT INTO dbo.TestTEXT WITH (TABLOCKX) ( padding ) SELECT CONVERT(TEXT, padding) FROM dbo.TestCHAR ORDER BY id ; -- ========== -- Space used -- ========== -- EXECUTE sys.sp_spaceused @objname = 'dbo.TestCHAR'; EXECUTE sys.sp_spaceused @objname = 'dbo.TestMAX'; EXECUTE sys.sp_spaceused @objname = 'dbo.TestTEXT'; ; CHECKPOINT ; That takes around 15 seconds to run, and shows the space allocated to each table in its output: To illustrate the points I want to make today, the example task we are going to set ourselves is to return a random set of 150 rows from each table.  The basic shape of the test query is the same for each of the three test tables: SELECT TOP (150) T.id, T.padding FROM dbo.Test AS T ORDER BY NEWID() OPTION (MAXDOP 1) ; Test 1 – CHAR(3999) Running the template query shown above using the TestCHAR table as the target, we find that the query takes around 5 seconds to return its results.  This seems slow, considering that the table only has 50,000 rows.  Working on the assumption that generating a GUID for each row is a CPU-intensive operation, we might try enabling parallelism to see if that speeds up the response time.  Running the query again (but without the MAXDOP 1 hint) on a machine with eight logical processors, the query now takes 10 seconds to execute – twice as long as when run serially. Rather than attempting further guesses at the cause of the slowness, let’s go back to serial execution and add some monitoring.  The script below monitors STATISTICS IO output and the amount of tempdb used by the test query.  We will also run a Profiler trace to capture any warnings generated during query execution. DECLARE @read BIGINT, @write BIGINT ; SELECT @read = SUM(num_of_bytes_read), @write = SUM(num_of_bytes_written) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; SET STATISTICS IO ON ; SELECT TOP (150) TC.id, TC.padding FROM dbo.TestCHAR AS TC ORDER BY NEWID() OPTION (MAXDOP 1) ; SET STATISTICS IO OFF ; SELECT tempdb_read_MB = (SUM(num_of_bytes_read) - @read) / 1024. / 1024., tempdb_write_MB = (SUM(num_of_bytes_written) - @write) / 1024. / 1024., internal_use_MB = ( SELECT internal_objects_alloc_page_count / 128.0 FROM sys.dm_db_task_space_usage WHERE session_id = @@SPID ) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; Let’s take a closer look at the statistics and query plan generated from this: Following the flow of the data from right to left, we see the expected 50,000 rows emerging from the Clustered Index Scan, with a total estimated size of around 191MB.  The Compute Scalar adds a column containing a random GUID (generated from the NEWID() function call) for each row.  With this extra column in place, the size of the data arriving at the Sort operator is estimated to be 192MB. Sort is a blocking operator – it has to examine all of the rows on its input before it can produce its first row of output (the last row received might sort first).  This characteristic means that Sort requires a memory grant – memory allocated for the query’s use by SQL Server just before execution starts.  In this case, the Sort is the only memory-consuming operator in the plan, so it has access to the full 243MB (248,696KB) of memory reserved by SQL Server for this query execution. Notice that the memory grant is significantly larger than the expected size of the data to be sorted.  SQL Server uses a number of techniques to speed up sorting, some of which sacrifice size for comparison speed.  Sorts typically require a very large number of comparisons, so this is usually a very effective optimization.  One of the drawbacks is that it is not possible to exactly predict the sort space needed, as it depends on the data itself.  SQL Server takes an educated guess based on data types, sizes, and the number of rows expected, but the algorithm is not perfect. In spite of the large memory grant, the Profiler trace shows a Sort Warning event (indicating that the sort ran out of memory), and the tempdb usage monitor shows that 195MB of tempdb space was used – all of that for system use.  The 195MB represents physical write activity on tempdb, because SQL Server strictly enforces memory grants – a query cannot ‘cheat’ and effectively gain extra memory by spilling to tempdb pages that reside in memory.  Anyway, the key point here is that it takes a while to write 195MB to disk, and this is the main reason that the query takes 5 seconds overall. If you are wondering why using parallelism made the problem worse, consider that eight threads of execution result in eight concurrent partial sorts, each receiving one eighth of the memory grant.  The eight sorts all spilled to tempdb, resulting in inefficiencies as the spilled sorts competed for disk resources.  More importantly, there are specific problems at the point where the eight partial results are combined, but I’ll cover that in a future post. CHAR(3999) Performance Summary: 5 seconds elapsed time 243MB memory grant 195MB tempdb usage 192MB estimated sort set 25,043 logical reads Sort Warning Test 2 – VARCHAR(MAX) We’ll now run exactly the same test (with the additional monitoring) on the table using a VARCHAR(MAX) padding column: DECLARE @read BIGINT, @write BIGINT ; SELECT @read = SUM(num_of_bytes_read), @write = SUM(num_of_bytes_written) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; SET STATISTICS IO ON ; SELECT TOP (150) TM.id, TM.padding FROM dbo.TestMAX AS TM ORDER BY NEWID() OPTION (MAXDOP 1) ; SET STATISTICS IO OFF ; SELECT tempdb_read_MB = (SUM(num_of_bytes_read) - @read) / 1024. / 1024., tempdb_write_MB = (SUM(num_of_bytes_written) - @write) / 1024. / 1024., internal_use_MB = ( SELECT internal_objects_alloc_page_count / 128.0 FROM sys.dm_db_task_space_usage WHERE session_id = @@SPID ) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; This time the query takes around 8 seconds to complete (3 seconds longer than Test 1).  Notice that the estimated row and data sizes are very slightly larger, and the overall memory grant has also increased very slightly to 245MB.  The most marked difference is in the amount of tempdb space used – this query wrote almost 391MB of sort run data to the physical tempdb file.  Don’t draw any general conclusions about VARCHAR(MAX) versus CHAR from this – I chose the length of the data specifically to expose this edge case.  In most cases, VARCHAR(MAX) performs very similarly to CHAR – I just wanted to make test 2 a bit more exciting. MAX Performance Summary: 8 seconds elapsed time 245MB memory grant 391MB tempdb usage 193MB estimated sort set 25,043 logical reads Sort warning Test 3 – TEXT The same test again, but using the deprecated TEXT data type for the padding column: DECLARE @read BIGINT, @write BIGINT ; SELECT @read = SUM(num_of_bytes_read), @write = SUM(num_of_bytes_written) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; SET STATISTICS IO ON ; SELECT TOP (150) TT.id, TT.padding FROM dbo.TestTEXT AS TT ORDER BY NEWID() OPTION (MAXDOP 1, RECOMPILE) ; SET STATISTICS IO OFF ; SELECT tempdb_read_MB = (SUM(num_of_bytes_read) - @read) / 1024. / 1024., tempdb_write_MB = (SUM(num_of_bytes_written) - @write) / 1024. / 1024., internal_use_MB = ( SELECT internal_objects_alloc_page_count / 128.0 FROM sys.dm_db_task_space_usage WHERE session_id = @@SPID ) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; This time the query runs in 500ms.  If you look at the metrics we have been checking so far, it’s not hard to understand why: TEXT Performance Summary: 0.5 seconds elapsed time 9MB memory grant 5MB tempdb usage 5MB estimated sort set 207 logical reads 596 LOB logical reads Sort warning SQL Server’s memory grant algorithm still underestimates the memory needed to perform the sorting operation, but the size of the data to sort is so much smaller (5MB versus 193MB previously) that the spilled sort doesn’t matter very much.  Why is the data size so much smaller?  The query still produces the correct results – including the large amount of data held in the padding column – so what magic is being performed here? TEXT versus MAX Storage The answer lies in how columns of the TEXT data type are stored.  By default, TEXT data is stored off-row in separate LOB pages – which explains why this is the first query we have seen that records LOB logical reads in its STATISTICS IO output.  You may recall from my last post that LOB data leaves an in-row pointer to the separate storage structure holding the LOB data. SQL Server can see that the full LOB value is not required by the query plan until results are returned, so instead of passing the full LOB value down the plan from the Clustered Index Scan, it passes the small in-row structure instead.  SQL Server estimates that each row coming from the scan will be 79 bytes long – 11 bytes for row overhead, 4 bytes for the integer id column, and 64 bytes for the LOB pointer (in fact the pointer is rather smaller – usually 16 bytes – but the details of that don’t really matter right now). OK, so this query is much more efficient because it is sorting a very much smaller data set – SQL Server delays retrieving the LOB data itself until after the Sort starts producing its 150 rows.  The question that normally arises at this point is: Why doesn’t SQL Server use the same trick when the padding column is defined as VARCHAR(MAX)? The answer is connected with the fact that if the actual size of the VARCHAR(MAX) data is 8000 bytes or less, it is usually stored in-row in exactly the same way as for a VARCHAR(8000) column – MAX data only moves off-row into LOB storage when it exceeds 8000 bytes.  The default behaviour of the TEXT type is to be stored off-row by default, unless the ‘text in row’ table option is set suitably and there is room on the page.  There is an analogous (but opposite) setting to control the storage of MAX data – the ‘large value types out of row’ table option.  By enabling this option for a table, MAX data will be stored off-row (in a LOB structure) instead of in-row.  SQL Server Books Online has good coverage of both options in the topic In Row Data. The MAXOOR Table The essential difference, then, is that MAX defaults to in-row storage, and TEXT defaults to off-row (LOB) storage.  You might be thinking that we could get the same benefits seen for the TEXT data type by storing the VARCHAR(MAX) values off row – so let’s look at that option now.  This script creates a fourth table, with the VARCHAR(MAX) data stored off-row in LOB pages: CREATE TABLE dbo.TestMAXOOR ( id INTEGER IDENTITY (1,1) NOT NULL, padding VARCHAR(MAX) NOT NULL,   CONSTRAINT [PK dbo.TestMAXOOR (id)] PRIMARY KEY CLUSTERED (id), ) ; EXECUTE sys.sp_tableoption @TableNamePattern = N'dbo.TestMAXOOR', @OptionName = 'large value types out of row', @OptionValue = 'true' ; SELECT large_value_types_out_of_row FROM sys.tables WHERE [schema_id] = SCHEMA_ID(N'dbo') AND name = N'TestMAXOOR' ; INSERT INTO dbo.TestMAXOOR WITH (TABLOCKX) ( padding ) SELECT SPACE(0) FROM dbo.TestCHAR ORDER BY id ; UPDATE TM WITH (TABLOCK) SET padding.WRITE (TC.padding, NULL, NULL) FROM dbo.TestMAXOOR AS TM JOIN dbo.TestCHAR AS TC ON TC.id = TM.id ; EXECUTE sys.sp_spaceused @objname = 'dbo.TestMAXOOR' ; CHECKPOINT ; Test 4 – MAXOOR We can now re-run our test on the MAXOOR (MAX out of row) table: DECLARE @read BIGINT, @write BIGINT ; SELECT @read = SUM(num_of_bytes_read), @write = SUM(num_of_bytes_written) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; SET STATISTICS IO ON ; SELECT TOP (150) MO.id, MO.padding FROM dbo.TestMAXOOR AS MO ORDER BY NEWID() OPTION (MAXDOP 1, RECOMPILE) ; SET STATISTICS IO OFF ; SELECT tempdb_read_MB = (SUM(num_of_bytes_read) - @read) / 1024. / 1024., tempdb_write_MB = (SUM(num_of_bytes_written) - @write) / 1024. / 1024., internal_use_MB = ( SELECT internal_objects_alloc_page_count / 128.0 FROM sys.dm_db_task_space_usage WHERE session_id = @@SPID ) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; TEXT Performance Summary: 0.3 seconds elapsed time 245MB memory grant 0MB tempdb usage 193MB estimated sort set 207 logical reads 446 LOB logical reads No sort warning The query runs very quickly – slightly faster than Test 3, and without spilling the sort to tempdb (there is no sort warning in the trace, and the monitoring query shows zero tempdb usage by this query).  SQL Server is passing the in-row pointer structure down the plan and only looking up the LOB value on the output side of the sort. The Hidden Problem There is still a huge problem with this query though – it requires a 245MB memory grant.  No wonder the sort doesn’t spill to tempdb now – 245MB is about 20 times more memory than this query actually requires to sort 50,000 records containing LOB data pointers.  Notice that the estimated row and data sizes in the plan are the same as in test 2 (where the MAX data was stored in-row). The optimizer assumes that MAX data is stored in-row, regardless of the sp_tableoption setting ‘large value types out of row’.  Why?  Because this option is dynamic – changing it does not immediately force all MAX data in the table in-row or off-row, only when data is added or actually changed.  SQL Server does not keep statistics to show how much MAX or TEXT data is currently in-row, and how much is stored in LOB pages.  This is an annoying limitation, and one which I hope will be addressed in a future version of the product. So why should we worry about this?  Excessive memory grants reduce concurrency and may result in queries waiting on the RESOURCE_SEMAPHORE wait type while they wait for memory they do not need.  245MB is an awful lot of memory, especially on 32-bit versions where memory grants cannot use AWE-mapped memory.  Even on a 64-bit server with plenty of memory, do you really want a single query to consume 0.25GB of memory unnecessarily?  That’s 32,000 8KB pages that might be put to much better use. The Solution The answer is not to use the TEXT data type for the padding column.  That solution happens to have better performance characteristics for this specific query, but it still results in a spilled sort, and it is hard to recommend the use of a data type which is scheduled for removal.  I hope it is clear to you that the fundamental problem here is that SQL Server sorts the whole set arriving at a Sort operator.  Clearly, it is not efficient to sort the whole table in memory just to return 150 rows in a random order. The TEXT example was more efficient because it dramatically reduced the size of the set that needed to be sorted.  We can do the same thing by selecting 150 unique keys from the table at random (sorting by NEWID() for example) and only then retrieving the large padding column values for just the 150 rows we need.  The following script implements that idea for all four tables: SET STATISTICS IO ON ; WITH TestTable AS ( SELECT * FROM dbo.TestCHAR ), TopKeys AS ( SELECT TOP (150) id FROM TestTable ORDER BY NEWID() ) SELECT T1.id, T1.padding FROM TestTable AS T1 WHERE T1.id = ANY (SELECT id FROM TopKeys) OPTION (MAXDOP 1) ; WITH TestTable AS ( SELECT * FROM dbo.TestMAX ), TopKeys AS ( SELECT TOP (150) id FROM TestTable ORDER BY NEWID() ) SELECT T1.id, T1.padding FROM TestTable AS T1 WHERE T1.id IN (SELECT id FROM TopKeys) OPTION (MAXDOP 1) ; WITH TestTable AS ( SELECT * FROM dbo.TestTEXT ), TopKeys AS ( SELECT TOP (150) id FROM TestTable ORDER BY NEWID() ) SELECT T1.id, T1.padding FROM TestTable AS T1 WHERE T1.id IN (SELECT id FROM TopKeys) OPTION (MAXDOP 1) ; WITH TestTable AS ( SELECT * FROM dbo.TestMAXOOR ), TopKeys AS ( SELECT TOP (150) id FROM TestTable ORDER BY NEWID() ) SELECT T1.id, T1.padding FROM TestTable AS T1 WHERE T1.id IN (SELECT id FROM TopKeys) OPTION (MAXDOP 1) ; SET STATISTICS IO OFF ; All four queries now return results in much less than a second, with memory grants between 6 and 12MB, and without spilling to tempdb.  The small remaining inefficiency is in reading the id column values from the clustered primary key index.  As a clustered index, it contains all the in-row data at its leaf.  The CHAR and VARCHAR(MAX) tables store the padding column in-row, so id values are separated by a 3999-character column, plus row overhead.  The TEXT and MAXOOR tables store the padding values off-row, so id values in the clustered index leaf are separated by the much-smaller off-row pointer structure.  This difference is reflected in the number of logical page reads performed by the four queries: Table 'TestCHAR' logical reads 25511 lob logical reads 000 Table 'TestMAX'. logical reads 25511 lob logical reads 000 Table 'TestTEXT' logical reads 00412 lob logical reads 597 Table 'TestMAXOOR' logical reads 00413 lob logical reads 446 We can increase the density of the id values by creating a separate nonclustered index on the id column only.  This is the same key as the clustered index, of course, but the nonclustered index will not include the rest of the in-row column data. CREATE UNIQUE NONCLUSTERED INDEX uq1 ON dbo.TestCHAR (id); CREATE UNIQUE NONCLUSTERED INDEX uq1 ON dbo.TestMAX (id); CREATE UNIQUE NONCLUSTERED INDEX uq1 ON dbo.TestTEXT (id); CREATE UNIQUE NONCLUSTERED INDEX uq1 ON dbo.TestMAXOOR (id); The four queries can now use the very dense nonclustered index to quickly scan the id values, sort them by NEWID(), select the 150 ids we want, and then look up the padding data.  The logical reads with the new indexes in place are: Table 'TestCHAR' logical reads 835 lob logical reads 0 Table 'TestMAX' logical reads 835 lob logical reads 0 Table 'TestTEXT' logical reads 686 lob logical reads 597 Table 'TestMAXOOR' logical reads 686 lob logical reads 448 With the new index, all four queries use the same query plan (click to enlarge): Performance Summary: 0.3 seconds elapsed time 6MB memory grant 0MB tempdb usage 1MB sort set 835 logical reads (CHAR, MAX) 686 logical reads (TEXT, MAXOOR) 597 LOB logical reads (TEXT) 448 LOB logical reads (MAXOOR) No sort warning I’ll leave it as an exercise for the reader to work out why trying to eliminate the Key Lookup by adding the padding column to the new nonclustered indexes would be a daft idea Conclusion This post is not about tuning queries that access columns containing big strings.  It isn’t about the internal differences between TEXT and MAX data types either.  It isn’t even about the cool use of UPDATE .WRITE used in the MAXOOR table load.  No, this post is about something else: Many developers might not have tuned our starting example query at all – 5 seconds isn’t that bad, and the original query plan looks reasonable at first glance.  Perhaps the NEWID() function would have been blamed for ‘just being slow’ – who knows.  5 seconds isn’t awful – unless your users expect sub-second responses – but using 250MB of memory and writing 200MB to tempdb certainly is!  If ten sessions ran that query at the same time in production that’s 2.5GB of memory usage and 2GB hitting tempdb.  Of course, not all queries can be rewritten to avoid large memory grants and sort spills using the key-lookup technique in this post, but that’s not the point either. The point of this post is that a basic understanding of execution plans is not enough.  Tuning for logical reads and adding covering indexes is not enough.  If you want to produce high-quality, scalable TSQL that won’t get you paged as soon as it hits production, you need a deep understanding of execution plans, and as much accurate, deep knowledge about SQL Server as you can lay your hands on.  The advanced database developer has a wide range of tools to use in writing queries that perform well in a range of circumstances. By the way, the examples in this post were written for SQL Server 2008.  They will run on 2005 and demonstrate the same principles, but you won’t get the same figures I did because 2005 had a rather nasty bug in the Top N Sort operator.  Fair warning: if you do decide to run the scripts on a 2005 instance (particularly the parallel query) do it before you head out for lunch… This post is dedicated to the people of Christchurch, New Zealand. © 2011 Paul White email: @[email protected] twitter: @SQL_Kiwi

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  • Did You Know? I gave two presentations last week

    - by Kalen Delaney
    Even though I didn't make it to TechEd this year, it didn't mean I was quiet last week. On Wednesday, I was in Colorado, giving a talk for the new Colorado PASS User Group, which is a joint venture between 3 different existing groups from Colorado Springs, Denver and Boulder. On Saturday, I spoke at SQL Saturday #43, in Redmond on the Microsoft campus. My presence there has already been mentioned on two other blogs here at SQLBlog: Merrill Aldrich and the infamous Buck Woody . As Merrill mentioned,...(read more)

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  • SQL Server 2014 – delayed transaction durability

    - by Michael Zilberstein
    As I’m downloading SQL Server 2014 CTP2 at this very moment, I’ve noticed new fascinating feature that hadn’t been announced in CTP1 : delayed transaction durability . It means that if your system is heavy on writes and on another hand you can tolerate data loss on some rare occasions – you can consider declaring transaction as DELAYED_DURABILITY = ON . In this case transaction would be committed when log is written to some buffer in memory – not to disk as usual. This way transactions can become...(read more)

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  • SQL TuneIn Zagreb 2014 – Session material

    - by Hugo Kornelis
    I spent the last few days in Zagreb, Croatie, at the third edition of the SQL TuneIn conference , and I had a very good time here. Nice company, good sessions, and awesome audiences. I presented my “Understanding Execution Plans” precon to a small but interested audience on Monday. Participants have received a download link for the slide deck. On Tuesday I had a larger crowd for my session on cardinality estimation. The slide deck and demo code used for that presentation will be available through...(read more)

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  • Did You Know? I gave two presentations last week

    - by Kalen Delaney
    Even though I didn't make it to TechEd this year, it didn't mean I was quiet last week. On Wednesday, I was in Colorado, giving a talk for the new Colorado PASS User Group, which is a joint venture between 3 different existing groups from Colorado Springs, Denver and Boulder. On Saturday, I spoke at SQL Saturday #43, in Redmond on the Microsoft campus. My presence there has already been mentioned on two other blogs here at SQLBlog: Merrill Aldrich and the infamous Buck Woody . As Merrill mentioned,...(read more)

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  • SQL?????!????????????????? ~ DBA????APEX

    - by Yuichi.Hayashi
    Oracle Application Express(Oracle APEX)????????????Web????????????????DBA??????·???????????????? SQL?????!????·????????????????????? SQL????????????SQL??????????????????????? Oracle Apex???????????????????????????????SQL??????????????????????????????????? Oracle DB10g????????????iSQLPLUS????????????????????????????????????? SQL?????????CSV???????????? ??·?????????????????????? ????: SQL??????????? ??????: SQL??????????? ?DESCRIBE?: ??????SQL?: SQL?????????????????????????????? ????: ?????SQL???????????? APEX?????????????????????????????????? APEX(Oracle Application Express)????~??????????????????????

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  • "If not exists" fails on SQL CE

    - by Mark Evans
    Hi I've got an unexpected problem. I'm making a script to update the schema on a SQL CE database. This won't run: if not exists ( Select column_name from information_schema.columns where column_name = 'TempTestField' and table_name = 'Inventory_Master_File' ) Alter table Inventory_Master_File add TempTestField nvarchar(10) null I think this is because I'm using stuff that isn't supported in SQL CE. Anyone know how to do this? I've tried rearranging the script and can't get anything to work. I tried "alter table ... where not exists ...". Note that the "select" part runs fine and also the "alter" part. The problem is "if not exists". I know there are some other postings regarding problems like this using SQL CE but I couldn't find an answer to this particular problem. Cheers Mark UPDATE: I've spent over an hour looking for a solution. I've found many postings asking for help with similar problems but I've still got no idea how to fix it. I really don't want to do this in C# code. I need to do this in a SQL script. I can't believe something this basic is causing so much difficulty :(

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  • How can I execute a .sql from C#?

    - by J. Pablo Fernández
    For some integration tests I want to connect to the database and run a .sql file that has the schema needed for the tests to actually run, including GO statements. How can I execute the .sql file? (or is this totally the wrong way to go?) I've found a post in the MSDN forum showing this code: using System.Data.SqlClient; using System.IO; using Microsoft.SqlServer.Management.Common; using Microsoft.SqlServer.Management.Smo; namespace ConsoleApplication1 { class Program { static void Main(string[] args) { string sqlConnectionString = "Data Source=(local);Initial Catalog=AdventureWorks;Integrated Security=True"; FileInfo file = new FileInfo("C:\\myscript.sql"); string script = file.OpenText().ReadToEnd(); SqlConnection conn = new SqlConnection(sqlConnectionString); Server server = new Server(new ServerConnection(conn)); server.ConnectionContext.ExecuteNonQuery(script); } } } but on the last line I'm getting this error: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. --- System.TypeInitializationException: The type initializer for '' threw an exception. --- .ModuleLoadException: The C++ module failed to load during appdomain initialization. --- System.DllNotFoundException: Unable to load DLL 'MSVCR80.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E). I was told to go and download that DLL from somewhere, but that sounds very hacky. Is there a cleaner way to? Is there another way to do it? What am I doing wrong? I'm doing this with Visual Studio 2008, SQL Server 2008, .Net 3.5SP1 and C# 3.0.

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  • SQL server 2005 agent not working

    - by flaggers
    Sql server 2005 service pack 2 version: 9.00.3042.00 All maintenance plans fail with the same error. The details of the error are:- Execute Maintenance Plan Execute maintenance plan. test7 (Error) Messages Execution failed. See the maintenance plan and SQL Server Agent job history logs for details. The advanced information section shows the following; Job 'test7.Subplan_1' failed. (SqlManagerUI) Program Location: at Microsoft.SqlServer.Management.SqlManagerUI.MaintenancePlanMenu_Run.PerformActions() At this point the following appear in the windows event log: Event Type: Error Event Source: SQLISPackage Event Category: None Event ID: 12291 Date: 28/05/2009 Time: 16:09:08 User: 'DOMAINNAME\username' Computer: SQLSERVER4 Description: Package "test7" failed. and also this: Event Type: Warning Event Source: SQLSERVERAGENT Event Category: Job Engine Event ID: 208 Date: 28/05/2009 Time: 16:09:10 User: N/A Computer: SQLSERVER4 Description: SQL Server Scheduled Job 'test7.Subplan_1' (0x96AE7493BFF39F4FBBAE034AB6DA1C1F) - Status: Failed - Invoked on: 2009-05-28 16:09:02 - Message: The job failed. The Job was invoked by User 'DOMAINNAME\username'. The last step to run was step 1 (Subplan_1). There are no entries in the SQl Agent log at all.

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  • SQL Server CE, Visual Studio 2008/2010 RC, and Linq-to-Sql

    - by blu
    I added an .sdf to my project, added a table, added a Linq-to-Sql dmbl, and tried to add the table to the dbml. The result was an error: "The selected object(s) are an unsupported data provider" This happens in both VS 2008 Professional SP1 and 2010 RC Ultimate. I found someone talking about using SQL Metal to generate the file, but I didn't enjoy that 2 years ago, and after a little playing around I recall why. Does anyone know if this is going to be supported in the release version? Should I abandon SQL Server CE and just use SQLite (with DbLinq)? Thanks for any insight.

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  • Nested SELECT clause in SQL Compact 3.5

    - by Sasha
    In this post "select with nested select" I read that SQL Compact 3.5 (SP1) support nested SELECT clause. But my request not work: t1 - table 1 t2 - table 2 c1, c2 = columns select t1.c1, t1.c2, (select count(t2.c1) from t2 where t2.id = t1.id) as count_t from t1 Does SQL Compact 3.5 SP1 support nested SELECT clause in this case? Update: SQL Compact 3.5 SP1 work with this type of nested request: SELECT ... from ... where .. IN (SELECT ...) SELECT ... from (SELECT ...)

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  • sql db problem with windows authentication

    - by Jimmy
    Have a SQL Server 2008 db which I connect to the Windows Authentication .. has worked good for 7-8 months .. but now when I come to work today it no longer worked to connect, without that I had done something Error message was: Can not open user default database. Login failed. Login failed for user 'Jimmy-PC \ Jimmy'. where the first is the computer name and the second is the user. The problem seems to be that it tries to connect to the default database. Have tried to change it without success .. I do not have sql server management tools for sql 2008 but only to 2005, someone who has similar experience? who have not touched anything said over the weekend and it worked last Friday without any problems.

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  • Write a sql to get the last data

    - by Lu Lu
    Hello everyone, I have a Realtime table with example data: Symbol Date Value ABC 1/3/2009 03:05:01 327 -- is last data for 'ABC' ABC 1/2/2009 03:05:01 326 ABC 1/2/2009 02:05:01 323 ABC 1/2/2009 01:05:01 313 BBC 1/3/2009 03:05:01 458 -- is last data for 'BBC' BBC 1/2/2009 03:05:01 454 BBC 1/2/2009 02:05:01 453 BBC 1/2/2009 01:05:01 423 Please help me to write a sql to return last data for all symbol. The result is: Symbol Date Value ABC 1/3/2009 03:05:01 327 BBC 1/3/2009 03:05:01 458 P/s: I use sql server 2005. And Realtime data is very big, please optimize the sql code. Thanks.

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  • Need help with SQL query on SQL Server 2005

    - by Avinash
    We're seeing strange behavior when running two versions of a query on SQL Server 2005: version A: SELECT otherattributes.* FROM listcontacts JOIN otherattributes ON listcontacts.contactId = otherattributes.contactId WHERE listcontacts.listid = 1234 ORDER BY name ASC version B: DECLARE @Id AS INT; SET @Id = 1234; SELECT otherattributes.* FROM listcontacts JOIN otherattributes ON listcontacts.contactId = otherattributes.contactId WHERE listcontacts.listid = @Id ORDER BY name ASC Both queries return 1000 rows; version A takes on average 15s; version B on average takes 4s. Could anyone help us understand the difference in execution times of these two versions of SQL? If we invoke this query via named parameters using NHibernate, we see the following query via SQL Server profiler: EXEC sp_executesql N'SELECT otherattributes.* FROM listcontacts JOIN otherattributes ON listcontacts.contactId = otherattributes.contactId WHERE listcontacts.listid = @id ORDER BY name ASC', N'@id INT', @id=1234; ...and this tends to perform as badly as version A.

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  • SQL Server ORDER BY/WHERE with nested select

    - by Echilon
    I'm trying to get SQL Server to order by a column from a nested select. I know this isn't the best way of doing this but it needs to be done. I have two tables, Bookings and BookingItems. BookingItems contains StartDate and EndDate fields, and there can be multiple BookingItems on a Booking. I need to find the earliest startdate and latest end date from BookingItems, then filter and sort by these values. I've tried with a nested select, but when I try to use one of the selected columns in a WHERE or ORDER BY, I get an "Invalid Column Name". SELECT b.*, (SELECT COUNT(*) FROM bookingitems i WHERE b.BookingID = i.BookingID) AS TotalRooms, (SELECT MIN(i.StartDate) FROM bookingitems i WHERE b.BookingID = i.BookingID) AS StartDate, (SELECT MAX(i.EndDate) FROM bookingitems i WHERE b.BookingID = i.BookingID) AS EndDate FROM bookings b LEFT JOIN customers c ON b.CustomerID = c.CustomerID WHERE StartDate >= '2010-01-01' Am I missing something about SQL ordering? I'm using SQL Server 2008.

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  • creating multiple users for a c#.net winform application using sql server express

    - by sqlchild
    i have a single sql database in sql server express. i have a login MAINLOGIN, for this database. i want insertion of data in this database through multiple users, U1,U2,U3, each having different userids & passwords. These users would be created by MAINLOGIN , manually or via the winform application. So while creating MAINLOGIN , i would give him permission to further create logins. For this what should i do? i cannot create MULTIPLE users, because for one database, only one user can be created under one login. so should i create multiple logins, L1,L2,L3, then map, U1, U2, U3 to them. Or, is there a better way to do this? like application roles etc. i dont want to use windows authentication. because if i know the system password, then i could simply connect sql via the application and insert wrong data.

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  • Use LINQ to SQL results inside SQL Server stored procedure

    - by ifwdev
    Note: I'm not trying to call a SQL Server stored proc using a L2SQL datacontext. I use LINQPad for some fairly complex "reporting" that takes L2SQL output saved to an Array and is processed further. For example, it's usually much easier to do multiple levels of grouping with LINQ to Objects instead of trying to optimize a T-SQL query to run in a reasonable amount of time. What would be the easiest way to take the end result of one of these "applications" and use that in a SQL Server 2008 stored proc? The idea is to use the data for a Reporting Services Report, rather than copying and pasting into Excel (manual labor). The reports need to be accessible on the report server (not using the Report Server control in an application). I could output CSV and read that somehow via command line exec, but that seems like a hack. Thanks for your help.

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  • Cannot login to SQL Server 2008 R2 with Windows authentication

    - by Ian Boyd
    When i try to connect to SQL Server (2008 R2) using Windows authentication: i cannot: Checking the Windows Application event log, i find the error: Login failed for user 'AVATOPIA\ian'. Reason: Token-based server access validation failed with an infrastructure error. Check for previous errors. [CLIENT: ] Log Name: Application Source: MSSQLSERVER Event ID: 18456 Level: Information User: AVATOPIA\ian OpCode: Task Category: Logon i can login to the computer itself using Windows authentication. i can log into SQL Server using the local Windows Administrator account. We can connect to 8 other SQL Servers on the domain using Windows Authentication. Just this one, whitch is the only one that is 2008 R2 is failing. So i assume it's a bug with *2008 R2. Note: i cannot logon locally, or remotely, using Windows authentication. i can login locally and remotely using SQL Server Authentication. Update Note: It's not limited to SQL Server Management Studio, standalone applications that connect using Windows authentication: fail: Note: It's not a client problem, as we can connect fine to other (non-SQL Server 2008 R2 machines): i'm sure there's a technote or knowledge base article describing why SQL Server 2008 R2 is broken by default, but i can't find it. Update 2 Matt figure out the change that Microsoft made so that SQL Server 2008 R2 is broken by default: Administrators are no longer administrators All that remains is to figure out how to make Administrators administrators. One of these days i'm going to start a list of changes around Microsoft's "broken by default" initiative. Steps to reproduce the problem How do i add a group to the sysadmin fixed server role? Here's the steps i try, that don't work: Click Add: Click Object Types: Ensure that you have no ability to add groups: and click OK. Under Enter the object names to select, enter Administrators: Click Check Names, and ensure that you are not allowed to add groups: and click Cancel. Click Browse..., and ensure that you have no ability to add groups: You should now still not have added any group to the sysadmin role. Additional information SQL Server Management Studio is being run as an administrator: SQL Server is set to use Windows Authentication: tried while logged into SQL with both sa and the only other sysadmin domain account (screenshot can be supplied for those who don't believe)

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  • SQL 2008 R2 Named Instance Client Connectivity Issues?

    - by Jerry Dodge
    We're upgrading our software from using SQL 2000 to 2008 R2. Our customers will be installing an update which uninstalls 2000 and installs 2008 R2 under the same instance. So if no instance existed, then no instance name will be set (default). However, the problem starts with the customers which have a named SQL instance. Starting in 2008 R2 (not sure of ones before), for some reason, a client connecting to the server by its instance name is unsuccessful. I'm testing from the Management Studio - if I can't connect this, then nothing can connect. I browse network servers, and find the specific server\instance in the list. But, upon trying to connect to an instance name like MyServer\INST, I get: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified) (Microsoft SQL Server, Error: -1) I do in fact have TCP/IP and Named Pipes protocols enabled, this is the first thing I did. When I connect to the server using a comma (,) and port number like MyServer, 49195, it works just fine. So it appears that client computers are just unable to identify the instance names. This has happened on all our installations of SQL 2008 R2 and from all client computers, including Win 7, XP, Vista, Server 2008, and Server 2003. We never experienced such issues on earlier versions of SQL. The problem even persists if the firewalls and antiviruses are all disabled. Now, this is a large update which we will be distributing soon to all our customers, and we want to minimize the interaction they need with us to get this installed. We absolutely hate the idea of using a port number, because it will always be different, and we would have to modify each client to point to this server/port. Some of our customers may have hundreds of client computers. How do I make client connections to a named SQL instance work again? After all, this is the whole purpose of named instances, and if a client can't connect to this instance by its name, then what is it even named for? EDIT It was mentioned to make sure SQL Browser is running, so I checked, and it is running. The server is also able to connect to its self (locally) - just external connections are refused. UPDATE After more careful checking, I learned the firewall wasn't completely disabled when testing, and upon disabling it completely, this works. So it appears that SQL Browser is being blocked by the firewall from external clients from accessing.

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  • SQL server agent job to execute SSIS package fails, package succeds if run manually

    - by growse
    I've got a SSIS package installed on a SQL server (SQL Server 2012). It's fairly simple and just fetches data from a remote data source and adds it into a local table. The remote connection string is using SQL server authentication, while the local connection is using Windows auth. The remote connection password is protected, and the package was imported setting the protection level to Rely on server storage and roles for access control. If I run the SSIS package manually, it works. If I run it from the command line using dtexec, it works. If I use runas to switch to the domain account that the SQL server agent is running under, and then run the package using dtexec, it works. If I create a SQL Agent job with a single step to run the package, it fails, providing very little detail as to what's going on. I'm guessing it's not able to get the password to log into the remote SQL server, because it fails very quickly. Also, if I tick 'log to table' and view the resulting file, I get the following: Description: ADO NET Source has failed to acquire the connection {0D8F2CD4-A763-4AEB-8B52-B8FAE0621ED3} with the following error message: "Login failed for user 'username'.". If I try to add the password in the connection string manually under data sources in the job step dialog, it refuses to save it, always seeming to remove the 'password' bit of the connection string. I thought that SQL server agent jobs always ran under the context of the account which the SQL server agent is running under. This account is a sysadmin on the local SQL server, and the package works using dtexec under that account, so why would it fail when trying to run as an agent job?

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  • SQL to select random mix of rows fairly [migrated]

    - by Matt Sieker
    Here's my problem: I have a set of tables in a database populated with data from a client that contains product information. In addition to the basic product information, there is also information about the manufacturer, and categories for those products (a product can be in one or more categories). These categories are then referred to as "Product Categories", and which stores these products are available at. These tables are updated once a week from a feed from the customer. Since for our purposes, some of the product categories are the same, or closely related for our purposes, there is another level of categories called "General Categories", a general category can have one or more product categories. For the scope of these tables, here's some rough numbers: Data Tables: Products: 475,000 Manufacturers: 1300 Stores: 150 General Categories: 245 Product Categories: 500 Mapping Tables: Product Category -> Product: 655,000 Stores -> Products: 50,000,000 Now, for the actual problem: As part of our software, we need to select n random products, given a store and a general category. However, we also need to ensure a good mix of manufacturers, as in some categories, a single manufacturer dominates the results, and selecting rows at random causes the results to strongly favor that manufacturer. The solution that is currently in place, works for most cases, involves selecting all of the rows that match the store and category criteria, partition them on manufacturer, and include their row number from within their partition, then select from that where the row number for that manufacturer is less than n, and use ROWCOUNT to clamp the total rows returned to n. This query looks something like this: SET ROWCOUNT 6 select p.Id, GeneralCategory_Id, Product_Id, ISNULL(m.DisplayName, m.Name) AS Vendor, MSRP, MemberPrice, FamilyImageName from (select p.Id, gc.Id GeneralCategory_Id, p.Id Product_Id, ctp.Store_id, Manufacturer_id, ROW_NUMBER() OVER (PARTITION BY Manufacturer_id ORDER BY NEWID()) AS 'VendorOrder', MSRP, MemberPrice, FamilyImageName from GeneralCategory gc inner join GeneralCategoriesToProductCategories gctpc ON gc.Id=gctpc.GeneralCategory_Id inner join ProductCategoryToProduct pctp on gctpc.ProductCategory_Id = pctp.ProductCategory_Id inner join Product p on p.Id = pctp.Product_Id inner join StoreToProduct ctp on p.Id = ctp.Product_id where gc.Id = @GeneralCategory and ctp.Store_id=@StoreId and p.Active=1 and p.MemberPrice >0) p inner join Manufacturer m on m.Id = p.Manufacturer_id where VendorOrder <=6 order by NEWID() SET ROWCOUNT 0 (I've tried to somewhat format it to make it cleaner, but I don't think it really helps) Running this query with an execution plan shows that for the majority of these tables, it's doing a Clustered Index Seek. There are two operations that take up roughly 90% of the time: Index Seek (Nonclustered) on StoreToProduct: 17%. This table just contains the key of the store, and the key of the product. It seems that NHibernate decided not to make a composite key when making this table, but I'm not concerned about this at this point, as compared to the other seek... Clustered Index Seek on Product: 69%. I really have no clue how I could make this one more performant. On categories without a lot of products, performance is acceptable (<50ms), however larger categories can take a few hundred ms, with the largest category taking 3s (which has about 170k products). It seems I have two ways to go from this point: Somehow optimize the existing query and table indices to lower the query time. As almost every expensive operation is already a clustered index scan, I don't know what could be done there. The inner query could be tuned to not return all of the possible rows for that category, but I am unsure how to do this, and maintain the requirements (random products, with a good mix of manufacturers) Denormalize this data for the purpose of this query when doing the once a week import. However, I am unsure how to do this and maintain the requirements. Does anyone have any input on either of these items?

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  • Importing Sql Server 2005 database into Sql Server express 2008

    - by Matthew Kanwisher
    Is there any way to import a database backup from 2005 into 2008 express edition. What I've had to resort to is doing a script the database, then import all the data through DTS. Whenever I tried to import straight from a backup file it says something about not being to import into a new version of sql server or I'll get the below error. title: Microsoft SQL Server Management Studio Specified cast is not valid. (SqlManagerUI)

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