Exam 70-765 topic 3 question 110 discussion

Actual exam question from Microsoft's 70-765

Question #: 110
Topic #: 3

Note: This question is part of a series of questions that present the same scenario. Each question in the series contains a unique solution that might meet the stated goals. Some question sets might have more than one correct solution, while others might not have a correct solution.
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You are tuning the performance of a virtual machines that hosts a Microsoft SQL Server instance.
The virtual machine originally had four CPU cores and now has 32 CPU cores.
The SQL Server instance uses the default settings and has an OLTP database named db1. The largest table in db1 is a key value store table named table1.
Several reports use the PIVOT statement and access more than 100 million rows in table1.
You discover that when the reports run, there are PAGELATCH_IO waits on PFS pages 2:1:1, 2:2:1, 2:3:1, and 2:4:1 within the tempdb database.
You need to prevent the PAGELATCH_IO waits from occurring.
Solution: You add more tempdb databases.
Does this meet the goal?

A. Yes
B. No

Show Suggested Answer

Suggested Answer: B 🗳️
From SQL Servers perspective, you can measure the I/O latency from sys.dm_os_wait_stats. If you consistently see high waiting for PAGELATCH_IO, you can benefit from a faster I/O subsystem for SQL Server.
A cause can be poor design of your database - you may wish to split out data located on 'hot pages', which are accessed frequently and which you might identify as the causes of your latch contention. For example, if you have a currency table with a data page containing 100 rows, of which 1 is updated per transaction and you have a transaction rate of 200/sec, you could see page latch queues of 100 or more. If each page latch wait costs just 5ms before clearing, this represents a full half-second delay for each update. In this case, splitting out the currency rows into different tables might prove more performant (if less normalized and logically structured).
References: https://www.mssqltips.com/sqlservertip/3088/explanation-of-sql-server-io-and-latches/

by DudeHere at April 12, 2020, 7:24 a.m.

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DudeHere

Highly Voted 5 years, 2 months ago

I just reread the question. It is not possible to add more tempdb DATABASES. If this is the solution, then of course the answer is B. If it is FILES, then this would reduce the pagelatch_IO issues.

upvoted 6 times

KC

4 years, 11 months ago

Agree, more tempdb files might help. https://support.microsoft.com/en-us/help/2154845/recommendations-to-reduce-allocation-contention-in-sql-server-tempdb-d

upvoted 2 times

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RohitRaj2311

Most Recent 4 years, 8 months ago

well, you can only have one tempdb. so B

upvoted 2 times

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Slava_bcd81

4 years, 8 months ago

if place additional tempdb file on a new drive I would choose A, but the question doesnt say that, so I think I rather choose B

upvoted 2 times

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DudeHere

5 years, 2 months ago

Going with B, I don't see any PAGELATCH_UP. to fix this issue would be to upgrade th disksubsystem. "page IO latch waits indicate slow IO response times; page latch update waits indicate incorrect file layout." https://docs.microsoft.com/en-us/sql/relational-databases/system-dynamic-management-views/sys-dm-os-wait-stats-transact-sql?view=sql-server-2017

upvoted 3 times

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DudeHere

5 years, 2 months ago

Answer is A "originally had four CPUs" , now has 32. PAGELATCH_IO waits on PFS pages show only 4 entries.... They are screaming that there are only max 4 files for tempdb. Increase to 8 and monitor, increasing by multiples of 4. https://support.microsoft.com/en-us/help/2154845/recommendations-to-reduce-allocation-contention-in-sql-server-tempdb-d

upvoted 1 times

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