Performance tuning tips for database developers

The DBA is not going to have time to scrutinize every change made to a stored procedure. Learning to do basic tuning might save you from reworking code late in the game.

Performance tuning is not easy and there aren’t any silver bullets, but you can go a surprisingly long way with a few basic guidelines.

Continue reading “Performance tuning tips for database developers”

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Database optimization tips for Developers and SQL Server DBAs

Database Optimization for Developers:

  1. If your application stops working suddenly, it may not be a database issue. For example, maybe you have a network problem. Investigate a bit before you accuse a DBA!
  2. Even if you’re a ninja SQL data modeler, ask a DBA to help you with your relational diagram. They have a lot to share and offer.
  3. DBAs don’t like rapid changes. This is natural: they need to analyze the database as a whole and examine the impact of any changes from all angles. A simple change in a column can take a week to be implemented—but that’s because an error could materialize as huge losses for the company. Be patient!
  4. Do not ask SQL DBAs to make data changes in a production environment. If you want access to the production database, you have to be responsible for all your own changes.

Database Optimization for SQL Server DBAs:

  1. If you don’t like people asking you about the database, give them a real-time status panel. Developers are always suspicious of a database’s status, and such a panel could save everyone time and energy.
  2. Help developers in a test/quality assurance environment. Make it easy to simulate a production server with simple tests on real-world data. This will be a significant time-saver for others as well as yourself.
  3. Developers spend all day on systems with frequently-changed business logic. Try to understand this world being more flexible, and be able to break some rules in a critical moment.
  4. SQL databases evolve. The day will come when you have to migrate your data to a new version. Developers count on significant new functionality with each new version. Instead of refusing to accept their changes, plan ahead and be ready for the migration.

Continue reading “Database optimization tips for Developers and SQL Server DBAs”

Deleting unused indexes from SQL server to free up space and improve performance

In SQL Server, indexes can be a double-edged sword. Sure, they can make queries run faster, but at the same time, their maintenance can have a negative impact. You can improve your server’s overall performance by only maintaining useful indexes – but finding the ones you don’t need can be quite a manual process.

If you see indexes where there are no seeks, scans or lookups, but there are updates this means that SQL Server has not used the index to satisfy a query but still needs to maintain the index.

Remember that the data from these DMVs is reset when SQL Server is restarted, so make sure you have collected data for a long enough period of time to determine which indexes may be good candidates to be dropped.

Run this in SQL Server:

SELECT OBJECT_NAME(S.[OBJECT_ID]) AS [OBJECT NAME], 
       I.[NAME] AS [INDEX NAME], 
       USER_SEEKS, 
       USER_SCANS, 
       USER_LOOKUPS, 
       USER_UPDATES 
FROM   SYS.DM_DB_INDEX_USAGE_STATS AS S 
       INNER JOIN SYS.INDEXES AS I ON I.[OBJECT_ID] = S.[OBJECT_ID] AND I.INDEX_ID = S.INDEX_ID 
WHERE  OBJECTPROPERTY(S.[OBJECT_ID],'IsUserTable') = 1
       AND S.database_id = DB_ID()

Here we can see seeks, scans, lookups and updates.

The seeks refer to how many times an index seek occurred for that index. A seek is the fastest way to access the data, so this is good.
The scans refers to how many times an index scan occurred for that index. A scan is when multiple rows of data had to be searched to find the data. Scans are something you want to try to avoid.
The lookups refer to how many times the query required data to be pulled from the clustered index or the heap (does not have a clustered index). Lookups are also something you want to try to avoid.
The updates refers to how many times the index was updated due to data changes which should correspond to the first query above.

To find the ones that can be safely removed, run this:

SELECT OBJECT_NAME(S.[OBJECT_ID]) AS [OBJECT NAME], 
       I.[NAME] AS [INDEX NAME], 
       USER_SEEKS, 
       USER_SCANS, 
       USER_LOOKUPS, 
       USER_UPDATES 
FROM   SYS.DM_DB_INDEX_USAGE_STATS AS S 
       INNER JOIN SYS.INDEXES AS I ON I.[OBJECT_ID] = S.[OBJECT_ID] AND I.INDEX_ID = S.INDEX_ID 
WHERE  OBJECTPROPERTY(S.[OBJECT_ID],'IsUserTable') = 1
AND OBJECT_NAME(S.[OBJECT_ID]) = '[your table name]'
       AND S.database_id = DB_ID() AND (USER_SEEKS = 0 AND USER_SCANS =0 AND USER_LOOKUPS=0)

You can then delete the unused indexes.

Get table size of the biggest tables in a database (SQL)

Following script will return a list of all the tables in your database with a size greater than 10MB.

SELECT 
    t.NAME AS TableName,
    s.Name AS SchemaName,
    p.rows AS RowCounts,
    SUM(a.total_pages) * 8 AS TotalSpaceKB, 
    CAST(ROUND(((SUM(a.total_pages) * 8) / 1024.00), 2) AS NUMERIC(36, 2)) AS TotalSpaceMB,
    SUM(a.used_pages) * 8 AS UsedSpaceKB, 
    CAST(ROUND(((SUM(a.used_pages) * 8) / 1024.00), 2) AS NUMERIC(36, 2)) AS UsedSpaceMB, 
    (SUM(a.total_pages) - SUM(a.used_pages)) * 8 AS UnusedSpaceKB,
    CAST(ROUND(((SUM(a.total_pages) - SUM(a.used_pages)) * 8) / 1024.00, 2) AS NUMERIC(36, 2)) AS UnusedSpaceMB
FROM 
    sys.tables t
INNER JOIN      
    sys.indexes i ON t.OBJECT_ID = i.object_id
INNER JOIN 
    sys.partitions p ON i.object_id = p.OBJECT_ID AND i.index_id = p.index_id
INNER JOIN 
    sys.allocation_units a ON p.partition_id = a.container_id
LEFT OUTER JOIN 
    sys.schemas s ON t.schema_id = s.schema_id
WHERE 
    t.NAME NOT LIKE 'dt%' 
    AND t.is_ms_shipped = 0
    AND i.OBJECT_ID > 255 
GROUP BY 
    t.Name, s.Name, p.Rows
	HAVING SUM(a.total_pages) * 8 / 1024.00 > 10
ORDER BY 
   TotalSpaceMB Desc

tableSize

Generate Create Statements for all indexes in a table

SELECT ' CREATE ' +
       CASE 
            WHEN I.is_unique = 1 THEN ' UNIQUE '
            ELSE ''
       END +
       I.type_desc COLLATE DATABASE_DEFAULT + ' INDEX ' +
       I.name + ' ON ' +
       SCHEMA_NAME(T.schema_id) + '.' + T.name + ' ( ' +
       KeyColumns + ' )  ' +
       ISNULL(' INCLUDE (' + IncludedColumns + ' ) ', '') +
       ISNULL(' WHERE  ' + I.filter_definition, '') + ' WITH ( ' +
       CASE 
            WHEN I.is_padded = 1 THEN ' PAD_INDEX = ON '
            ELSE ' PAD_INDEX = OFF '
       END + ',' +
       'FILLFACTOR = ' + CONVERT(
           CHAR(5),
           CASE 
                WHEN I.fill_factor = 0 THEN 100
                ELSE I.fill_factor
           END
       ) + ',' +
       -- default value 
       'SORT_IN_TEMPDB = OFF ' + ',' +
       CASE 
            WHEN I.ignore_dup_key = 1 THEN ' IGNORE_DUP_KEY = ON '
            ELSE ' IGNORE_DUP_KEY = OFF '
       END + ',' +
       CASE 
            WHEN ST.no_recompute = 0 THEN ' STATISTICS_NORECOMPUTE = OFF '
            ELSE ' STATISTICS_NORECOMPUTE = ON '
       END + ',' +
       ' ONLINE = OFF ' + ',' +
       CASE 
            WHEN I.allow_row_locks = 1 THEN ' ALLOW_ROW_LOCKS = ON '
            ELSE ' ALLOW_ROW_LOCKS = OFF '
       END + ',' +
       CASE 
            WHEN I.allow_page_locks = 1 THEN ' ALLOW_PAGE_LOCKS = ON '
            ELSE ' ALLOW_PAGE_LOCKS = OFF '
       END + ' ) ON [' +
       DS.name + ' ] ' +  CHAR(13) + CHAR(10) + ' GO' [CreateIndexScript]
FROM   sys.indexes I
       JOIN sys.tables T
            ON  T.object_id = I.object_id
       JOIN sys.sysindexes SI
            ON  I.object_id = SI.id
            AND I.index_id = SI.indid
       JOIN (
                SELECT *
                FROM   (
                           SELECT IC2.object_id,
                                  IC2.index_id,
                                  STUFF(
                                      (
                                          SELECT ' , ' + C.name + CASE 
                                                                       WHEN MAX(CONVERT(INT, IC1.is_descending_key)) 
                                                                            = 1 THEN 
                                                                            ' DESC '
                                                                       ELSE 
                                                                            ' ASC '
                                                                  END
                                          FROM   sys.index_columns IC1
                                                 JOIN sys.columns C
                                                      ON  C.object_id = IC1.object_id
                                                      AND C.column_id = IC1.column_id
                                                      AND IC1.is_included_column = 
                                                          0
                                          WHERE  IC1.object_id = IC2.object_id
                                                 AND IC1.index_id = IC2.index_id
                                          GROUP BY
                                                 IC1.object_id,
                                                 C.name,
                                                 index_id
                                          ORDER BY
                                                 MAX(IC1.key_ordinal) 
                                                 FOR XML PATH('')
                                      ),
                                      1,
                                      2,
                                      ''
                                  ) KeyColumns
                           FROM   sys.index_columns IC2 
                                  --WHERE IC2.Object_id = object_id('Person.Address') --Comment for all tables
                           GROUP BY
                                  IC2.object_id,
                                  IC2.index_id
                       ) tmp3
            )tmp4
            ON  I.object_id = tmp4.object_id
            AND I.Index_id = tmp4.index_id
       JOIN sys.stats ST
            ON  ST.object_id = I.object_id
            AND ST.stats_id = I.index_id
       JOIN sys.data_spaces DS
            ON  I.data_space_id = DS.data_space_id
       JOIN sys.filegroups FG
            ON  I.data_space_id = FG.data_space_id
       LEFT JOIN (
                SELECT *
                FROM   (
                           SELECT IC2.object_id,
                                  IC2.index_id,
                                  STUFF(
                                      (
                                          SELECT ' , ' + C.name
                                          FROM   sys.index_columns IC1
                                                 JOIN sys.columns C
                                                      ON  C.object_id = IC1.object_id
                                                      AND C.column_id = IC1.column_id
                                                      AND IC1.is_included_column = 
                                                          1
                                          WHERE  IC1.object_id = IC2.object_id
                                                 AND IC1.index_id = IC2.index_id
                                          GROUP BY
                                                 IC1.object_id,
                                                 C.name,
                                                 index_id 
                                                 FOR XML PATH('')
                                      ),
                                      1,
                                      2,
                                      ''
                                  ) IncludedColumns
                           FROM   sys.index_columns IC2 
                                  --WHERE IC2.Object_id = object_id('Person.Address') --Comment for all tables
                           GROUP BY
                                  IC2.object_id,
                                  IC2.index_id
                       ) tmp1
                WHERE  IncludedColumns IS NOT NULL
            ) tmp2
            ON  tmp2.object_id = I.object_id
            AND tmp2.index_id = I.index_id
WHERE  I.is_primary_key = 0
       AND I.is_unique_constraint = 0
           AND I.Object_id = object_id('tblERPInvoiceData') --Comment for all tables
           --AND I.name = 'IX_Address_PostalCode' --comment for all indexes

 
There is also one more on SQL Server Central:

https://www.sqlservercentral.com/Forums/Topic401784-562-3.aspx#bm1171799