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Category: Administration

Restoring A Striped Backup

Published 2016-03-11 by Kevin Feasel

Steve Jones shows us how to restore a backup striped across multiple files:

Each of these is part of a striped backup, a piece of a backup file. To restore the backup, I need all the files to reassemble the backup. This is fairly simple, but you should be aware of how this works and how to perform a restore.

In my case, you can see I have 7 files for each database. They are the same name with an _0x at the end, with x being the number of the file.

Take Steve’s advice and script out the restore process.  That way you know how to do it next time, can start building automation scripts, and can make your life easier.

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Are Trace Flags Dead?

Published 2016-03-10 by Kevin Feasel

Brent Ozar notes that several common trace flags are getting turned into all-grown-up commands:

SQL Server 2016 does away with these unintuitive trace flags by adding new ALTER DATABASE commands:

ALTER DATABASE SET MIXED_PAGE_ALLOCATION ON (or OFF, which is the new default behavior)

ALTER DATABASE MODIFY FILEGROUP [myfilegroup] AUTOGROW_ALL_FILES (or AUTOGROW_SINGLE_FILE, which is still the default)

I think trace flags will still be around for quite some time as a troubleshooting mechanism, but I certainly prefer clearer naming (was that trace flag 1117…or 1171…or maybe…).

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Get SQL Server Configuration Aliases

Published 2016-03-10 by Kevin Feasel

Chris Bell shows us how to get the list of aliases set up on a server:

It is also a pain to sit and transcribe the various alias settings to be able to rebuild them all on the next machine.

There is an export list option for the aliases on your server, that’s nice and all, but there isn’t a corresponding import option.

Plus you have to deal with 32 and 64 bit lists.

The very simple script below helps since you can use to get the details of both the 32 and 64bit SQL Server aliases you have setup on your system.

Ready for it? It’s a long convoluted one:

If you use server aliases, you’ll want to check out this script.

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Why Use Instant File Initialization?

Published 2016-03-09 by Kevin Feasel

Erin Stellato shows the benefits to using Instant File Initialization in terms of file modification and database restoration:

The time to zero out a file and write data is a function of sequential write performance on the drive(s) where the SQL Server data file(s) are located, when IFI is not enabled.  When IFI is enabled, creating or growing a data file is so fast that the time is not of significant consequence.  The time it takes to create or grow a value varies in seconds between 15K, SSD, flash, and magnetic storage when IFI is enabled.  However, if you do not enable IFI, there can be drastic differences in create, grow, and restore times depending on storage.

There’s a huge performance benefit with turning IFI on.

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DBCC UPDATEUSAGE

Published 2016-03-07 by Kevin Feasel

Slava Murygin has some information on the DBCC UPDATEUSAGE command:

As you can see, UPDATEUSAGE found three problems with that table, while was running in “ESTIMATEONLY” mode. When it run in “Fix” mode it also found and fixed only three problems. The number of rows was still left unfixed.

I think it’s fair to say that this is a relatively uncommonly-used DBCC command, but can definitely be useful in a subset of circumstances.

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CPU Co-Stop

Published 2016-03-04 by Kevin Feasel

David Klee discusses an important hypervisor-level metric:

VMware’s CPU Co-Stop metric shows you the amount of time that a parallelized request spends trying to line up the vCPU schedulers for the simultaneous execution of a task on multiple vCPUs. It’s measured in milliseconds spent in the queue per vCPU per polling interval. Higher is bad. Very bad. The operating system is constantly reviewing the running processes, and checking their runtime states. It can detect that a CPU isn’t keeping up with the others, and might actually flag a CPU is actually BAD if it can’t keep up and the difference is too great.

This is extremely useful information for DBAs in virtualized environments.  My crude and overly simplistic answer is, don’t over-book vCPUs on hosts running important VMs like your SQL Server instances.

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Auto-Update Stats Threshold Change

Published 2016-03-03 by Kevin Feasel

Erik Darling points out that automatic statistics updates will happen more frequently in 2016 for large tables than in prior versions:

Here’s an abridged version of 10-20 million and 30-40 million rows, and how many modifications they took before a stats update occurred. If you follow the PercentMod column down, the returns diminish a bit the higher up you get. I’m not saying that I’d prefer to wait for 20% + 500 rows to modify, by any stretch. My only point here is that there’s not a set percentage to point to.

And, because you’re probably wondering, turning on Trace Flag 2371 in 2016 doesn’t make any difference.

This is a good change, though as Erik points out, if you’re managing very large tables, you might already have the trace flag on and thereby won’t see any difference.

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DBCC Extended Checks

Published 2016-03-02 by Kevin Feasel

The SQL Server CSS team has a new post on DBCC performance improvements:

Starting with SQL Server 2016, additional checks on filtered indexes, persisted computed columns, and UDT columns will not be run by default to avoid the expensive expression evaluation(s.)  This change greatly reduces the duration of CHECKDB against databases containing these objects.  However, the physical consistency checks of these objects is always completed.  Only when EXTENDED_LOGICAL_CHECKS option is specified will the expression evaluations be performed in addition to already present, logical checks (indexed view, XML indexes, and spatial indexes) as part of the EXTENDED_LOGICAL_CHECKS option.

 

For filtered indexes, CHECKDB has also been improved to skip records that do not qualify as being indexed by target NC index. 

This is telling me that we’ll want to have two separate CHECKDB processes, one which regularly runs CHECKDB (or CHECKTABLE) and one which occasionally runs CHECKDB with EXTENDED_LOGICAL_CHECKS.

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Table Partitioning

Published 2016-03-02 by Kevin Feasel

Slava Murygin walks through partitioning:

Usually new Partition Ranges are added to the end of a Function/Schema, but in my example I’ll demonstrate how to split middle Partition.
At first we create new File Group. Then make it next within a schema and then split a Function:

All records, which are Less than 1/1/2015 and more than 1/1/2014, were moved to the new partition.

Partitioning is one of those topics I run into frequently enough to need to know it, but not frequently enough to memorize it; every time it feels like I’m starting from scratch.

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