How to increase SQL Query performance without changing the query - sql

Question

I have a project where I have very complex queries (Legacy project)
There are a lot of queries, stored procedures in the project, etc.
Queries have anywhere from 10-30 joins and slow filtering.
Project cannot be modified right away (Will take at least a year worth of work)
Is there a hardware way to increase performance. Can I use some smart Azure setup with increased computing power to increase speed?
Or what things do I need to look for in a physical server?

Answer 1

Avoid Multiple Joins in a Single Query.
Eliminate Cursors from the Query.
Avoid Use of Non-correlated
Scalar Sub Query.
Avoid Multi-statement Table Valued Functions (TVFs).
Creation and Use of Indexes.
Understand the Data.
Create a Highly Selective Index Filter data separately in hash table
from actual table
Do for every table that contains huge data then apply join on hash
tables rather actual tables in store procedure to combine the result.

Answer 2

Hardware approaches:
More RAM on motherboard and disk controller.
Additional processors (may require a different SQL Server license).
Faster storage devices.
If data is on an external SAN device, consider switching to a device with a faster connection type (Fibre Channel vs iSCSI, ATA over Ethernet (AoE), or HyperSCSI)

Answer 3

You can scale your performance with Azure using Standard and Premium subscriptions. So if you have slow queries you can always throw more hardware at it while you have the benefit of doing so only when needed. You can set your database to automatically scale, so when you're demand is low you pay less and when it's high your workload doesn't suffer.
Azure provides QPI, that basically identifies which of your queries are the most expensive ones so you can optimize them first.
Azure also provides different advisors, like index advisor, that will learn how you use your database and advise indexes to be created or dropped - the best thing about this is that it can do it automatically for you.
If you're thinking in on-prem solution you should consider the operating system cost and hardware cost as well and the time and cost of setting this up and configuring properly. Creating geo-replicated settings can add another level of complexity. So if you need to start fresh and your business requirements allow cloud services I'd say Azure is the way to go since it provides rich telemetry and all kinds of smart database capabilities (and they are coming month after month). Also don't forget that Azure is updated roughly every month while box editions get cumulative update packages after half a year or more.

Answer 4

hardware is very important, the better the faster.
but also you need to check your queries with aspect of performance.
for example,
check for missing indexes with actual execution plans. if there is,
you must add.
learn how to read execution plans & STATICS. cpu cost
is important. table-scans are deadly :) do not use.
rebuild indexes frequently.
if you are using ms-sql, you need "NOLOCK" property
after tables, otherwise you lock your table while reading/select.
when you are joining table, try to add your conditions on join. not
"where clause"
for example
SELECT * FROM TABLE A WITH (NOLOCK) INNER JOIN TABLE B WITH (NOLOCK)
ON A.ID = B.ID
WHERE B.SOMECOLUMN IS NOT NULL
SELECT * FROM TABLE A WITH (NOLOCK) INNER JOIN TABLE B WITH (NOLOCK)
ON A.ID = B.ID AND B.SOMECOLUMN IS NOT NULL
second one is better.
avoid "ORDER BY", "DISTINCT", if not necessary.
:)