Monthly Archives: September 2017

Get Index Column Info with Includes for One or Many Tables

— by Lori Brown @SQLSupahStah

I was recently working with one of my clients on some low hanging fruit type of query tuning. We had checked the cache for plans with missing index warnings in them and were trying to see if we could tweak and existing index or add a new index to speed things up. If you ever work with missing indexes, you surely have seen it recommend crazy things, duplicates or existing indexes or it wants something that can be added to an existing index.

The bottom line for missing index recommendations is that you should NEVER, EVER create a missing index unless you know for absolutely sure that the index does not exist and that it will really help a known performance issue. For instance, you can have missing index warnings on small tables that only return a couple of rows to the query. Those are usually not worth working on since scanning a small table can usually be done very quickly by SQL. To this day, I still find many databases that are way over indexed with indexes that were implemented simply because someone found a missing index warning and did not do their homework or they ran the dreaded Database Tuning Advisor which shoved a bunch of duplicate indexes into tables.

If you are wondering how to get a list of missing indexes, please check out Jeff Schwartz’s blog post on how to do this. (https://blog.sqlrx.com/2017/06/02/query-tuning-and-missing-index-recommendations/ ) This will give you a place to start. It is better if you know what query is throwing the missing index warning so it is a good idea to collect those either in a trace or extended events. Jeff builds on his first post and in his second post on the subject (https://blog.sqlrx.com/2017/07/20/handling-multiple-missing-index-recommendations-for-the-same-table/ ) also goes over the fun of having multiple missing index recommendations for a single table and how to deal with them.

Here’s a handy set of links for some of Jeff’s great index tuning work that you should really check out:

https://blog.sqlrx.com/2016/01/28/sql-server-20122014-extended-events-for-developers-part-1/

https://blog.sqlrx.com/2017/06/02/query-tuning-and-missing-index-recommendations/

https://blog.sqlrx.com/2017/07/20/handling-multiple-missing-index-recommendations-for-the-same-table/

https://blog.sqlrx.com/2017/08/10/how-indexing-affects-deletion-queries/

One of the things that I usually need when performance tuning is to know information about the existing indexes on specific tables. I always want to know what columns are in the indexes along with the included columns so that I can compare the existing indexes to the missing recommendations. This way I can better figure out if a recommendation is something that can be added to an existing index (like an included column) or if I really need to create a brand new index if it does not exist at all.

Like most DBA’s, I keep a toolkit with all kinds of handy scripts. However, I did not have one that would give me index included columns. I also wanted the query to be able to return info from one or many tables at the same time. This would be useful when dealing with things with lots of joins. I know that there are a few bloggers who have posted something similar but I wanted to have the ability to filter on one or multiple tables. So, here is what I came up with:

/********************************

Returns index columns with included columns

plus other needed index info for tables

in @tablelist variable

*********************************/

 

DECLARE @tablelist VARCHAR(1000)

DECLARE @sqlstr NVARCHAR(MAX)

 

SET @tablelist = ‘InvoiceLines,OrderLines,StockItemHoldings’ — comma delimited list of tables, can be one or multiples EX: ‘mytable’ or ‘mytable,nothertable,thirdtable’

 

— Query the tables

IF @tablelist <> OR @tablelist <> ‘?,?,?’

BEGIN

SET @tablelist = REPLACE(QUOTENAME(@tablelist,””), ‘,’, ”’,”’) — Add quotes so the IN clause will work

 

SET @sqlstr = ‘SELECT SCHEMA_NAME(o.schema_id) AS SchemaName

       ,o.name AS TableName

       ,i.name AS IndexName

       ,i.type_desc AS IndexType

       ,c.name AS ColumnName

       ,ic.is_included_column

       ,ic.index_column_id

       ,t.name

       ,c.max_length

       ,c.precision

       ,c.scale

FROM sys.indexes i

JOIN sys.index_columns ic ON i.index_id = ic.index_id

JOIN sys.columns c ON ic.column_id = c.column_id AND ic.object_id = c.object_id

JOIN sys.objects o ON o.object_id = i.object_id AND c.object_id = i.object_id

JOIN sys.types t on t.user_type_id = c.user_type_id

WHERE o.name IN (‘+@tablelist+‘)

ORDER BY SchemaName, TableName, IndexName, index_column_id’

 

EXEC sp_executesql @sqlstr

–PRINT @sqlstr

END

All you have to provide is a comma separated list of the table(s) you are interested in for the @tablelist variable and it will do the rest. The output looks like this:

Blog_20170928_1

I found several bloggers who had made queries that would concatenate the columns together but truthfully I found those hard to read so I settled for a list with some extra info on the data and index types. Hope this is useful to someone out there.

For more information about blog posts, concepts and definitions, further explanations, or questions you may have…please contact us at SQLRx@sqlrx.com. We will be happy to help! Leave a comment and feel free to track back to us. Visit us at www.sqlrx.com!

 

Find Tables That Have Special Features Enabled

Find out if any of tables in your database have special features enabled using the queries below.  These features need to be understood and carefully managed.

— CDC Enabled Tables

select distinct t.name AS CDCTables

from sys.tables t

where t.is_tracked_by_cdc = 1

 

— File Tables — SQL 2012 +

select distinct t.name AS FileTables

from sys.tables t

where t.is_filetable = 1

 

— Temporal Tables — SQL 2016 +

select distinct t.name AS TemporalTables

from sys.tables t

where t.temporal_type > 0

 

— Stretch Enabled Tables — SQL 2016 +

select distinct t.name AS StretchTables

from sys.tables t

where t.is_remote_data_archive_enabled > 0

 

— External Tables — SQL 2016 +

select distinct t.name AS ExternalTables

from sys.tables t

where t.is_external > 0

https://docs.microsoft.com/en-us/sql/relational-databases/track-changes/about-change-data-capture-sql-server

https://docs.microsoft.com/en-us/sql/relational-databases/blob/filetables-sql-server

https://docs.microsoft.com/en-us/sql/relational-databases/tables/temporal-tables

https://docs.microsoft.com/en-us/sql/sql-server/stretch-database/enable-stretch-database-for-a-table

https://docs.microsoft.com/en-us/sql/t-sql/statements/create-external-table-transact-sql

For more information about blog posts, concepts and definitions, further explanations, or questions you may have…please contact us at SQLRx@sqlrx.com. We will be happy to help! Leave a comment and feel free to track back to us. Visit us at www.sqlrx.com!

Find Out Who Changed the Database Recovery Model

— By Lori Brown @SQLSupahStah

I ran into a situation where we were working on a migration and had been directed to put all databases into FULL recovery model in anticipation of using log shipping to push databases to the new server. Once we are ready to go live on the new server the plan was to ship the last transaction logs and then restore them WITH RECOVERY in an effort to make the final cutover as quick as possible. Of course this means that we had to make sure that all databases were having regular log backups, which we did. Things were going along nicely until we started receiving log backup failure notifications.

Upon checking things, we found that one of the databases had been changed to SIMPLE recovery model. You can find this type of information in the default trace or you can simply scroll through the SQL error logs until you find the entry that you are looking for. If you have a busy instance that has a lot of entries in the error log, this can be a bit time consuming so I came up with a set of queries that will grab the error log entry and attempt to tie it to the info in the default trace so that it was easier to identify WHO was the culprit who made an unauthorized change to the database properties.

 

DECLARE @tracefile VARCHAR(500)

DECLARE @ProcessInfoSPID VARCHAR(20)

 

CREATE TABLE [dbo].[#SQLerrorlog](

[LogDate] DATETIME NULL,

[ProcessInfo] VARCHAR(10) NULL,

[Text] VARCHAR(MAX) NULL

)

 

/*

Valid parameters for sp_readerrorlog

1 – Error log: 0 = current, 1 = Archive #1, 2 = Archive #2, etc…

2 – Log file type: 1 or NULL = error log, 2 = SQL Agent log

3 – Search string 1

4 – Search string 2

 

Change parameters to meet your needs

*/

— Read error log looking for the words RECOVERY

–and either FULL, SIMPLE or BULK_LOGGED indicating a change from prior state

INSERT INTO #SQLerrorlog

EXEC sp_readerrorlog 0, 1, ‘RECOVERY’, ‘FULL’

 

INSERT INTO #SQLerrorlog

EXEC sp_readerrorlog 0, 1, ‘RECOVERY’, ‘SIMPLE’

 

INSERT INTO #SQLerrorlog

EXEC sp_readerrorlog 0, 1, ‘RECOVERY’, ‘BULK_LOGGED’

 

UPDATE #SQLerrorlog

SET ProcessInfo = SUBSTRING(ProcessInfo,5,20)

FROM #SQLerrorlog

WHERE ProcessInfo LIKE ‘spid%’

 

— Get path of default trace file

SELECT @tracefile = CAST(value AS VARCHAR(500))

FROM sys.fn_trace_getinfo(DEFAULT)

WHERE traceid = 1

AND property = 2

 

— Get objects altered from the default trace

SELECT IDENTITY(int, 1, 1) AS RowNumber, *

INTO #temp_trc

FROM sys.fn_trace_gettable(@tracefile, default) g — default = read all trace files

WHERE g.EventClass = 164

 

SELECT t.DatabaseID, t.DatabaseName, t.NTUserName, t.NTDomainName,

t.HostName, t.ApplicationName, t.LoginName, t.SPID, t.StartTime, l.Text

FROM #temp_trc t

JOIN #SQLerrorlog l ON t.SPID = l.ProcessInfo

WHERE t.StartTime > GETDATE()-1 — filter by time within the last 24 hours

ORDER BY t.StartTime DESC

 

DROP TABLE #temp_trc

DROP TABLE #SQLerrorlog

GO

 

You can find more on the following:

sp_readerrorlog is an undocumented procedure that actually uses xp_readerrorlog – https://www.mssqltips.com/sqlservertip/1476/reading-the-sql-server-log-files-using-tsql/

sys.fn_trace_getinfo – https://docs.microsoft.com/en-us/sql/relational-databases/system-functions/sys-fn-trace-getinfo-transact-sql

sys.fn_trace_gettable – https://docs.microsoft.com/en-us/sql/relational-databases/system-functions/sys-fn-trace-gettable-transact-sql

For more information about blog posts, concepts and definitions, further explanations, or questions you may have…please contact us at SQLRxSupport@sqlrx.com. We will be happy to help! Leave a comment and feel free to track back to us. We love to talk tech with anyone in our SQL family!

Links for new DMV’s in SQL 2017

Since we at SQLRX have been super busy this week and still need to do something for a blog post, I thought that doing a link round up of new dynamic management views that are going to be available in SQL 2017 would be a quick and good idea. I am really interested in sys.dm_db_log_info since it give VLF info and can be used for monitoring and alerting.

Enjoy!

Change:

A column on sys.dm_db_file_space_usage has been changed: https://docs.microsoft.com/en-us/sql/relational-databases/system-dynamic-management-views/sys-dm-db-file-space-usage-transact-sql

Brand new dmv’s:

sys.dm_db_log_stats https://docs.microsoft.com/en-us/sql/relational-databases/system-dynamic-management-views/sys-dm-db-log-stats-transact-sql

sys.dm_db_log_info https://docs.microsoft.com/en-us/sql/relational-databases/system-dynamic-management-views/sys-dm-db-log-info-transact-sql

sys.dm_db_stats_histogram https://docs.microsoft.com/en-us/sql/relational-databases/system-dynamic-management-views/sys-dm-db-stats-histogram-transact-sql

sys.dm_tran_version_store_space_usage https://docs.microsoft.com/en-us/sql/relational-databases/system-dynamic-management-views/sys-dm-tran-version-store-space-usage

sys.dm_os_host_info https://docs.microsoft.com/en-us/sql/relational-databases/system-dynamic-management-views/sys-dm-os-host-info-transact-sql

Blog_20170901_1

Yee Haw!!!!

For more information about blog posts, concepts and definitions, further explanations, or questions you may have…please contact us at SQLRx@sqlrx.com. We will be happy to help! Leave a comment and feel free to track back to us. Visit us at www.sqlrx.com!