Month: May 2021

Tuning SQL Server Queries 101

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First, get an actual query execution plan. Look for warnings in the query plan.

Basic

  • First look for large scans and lookups: these can often be resolved by creating a new index or extending an existing one with additional included columns. Seeks are usually preferable to scans.
  • Then look for significant variance of Actual versus Estimated row counts: you can provide the optimiser with more accurate information by updating statistics, creating new statistics objects, adding statistics on computed columns, or by breaking the query up into simpler parts. Might be caused by ‘parameter sniffing’.
  • Then look for expensive operators in the query plan, especially those that consume memory such as sorts and hashes. Sorting can sometimes be avoided by altering/adding indexes.

More Advanced

Joe Sack has an excellent walkthrough here: The Case of the Cardinality Estimate Red Herring

SQLFrontline Freemium Edition

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I’ve recently changed what I was calling the ‘Demo’ version of SQLFrontline, to a ‘Freemium’ model. The demo version only displayed one recommendation result in each of the four severity categories (Critical, High, Medium, Info).

The free version does not include all the features of the paid premium version obviously, but still provides some useful recommendations, providing advice on 40 checks.

Both use the same lightweight metadata collection.

The Free Version:

  • Performs 40 checks (out of 350+), but doesn’t show all affected objects if a check results in a recommendation
  • Deletes all collected metadata after collection
  • No reminder list is shown
  • Does not display a list of issues that are no longer present since last collection
  • Sends a single email for all servers
  • No database specific recommendations are made
  • Can only collect metadata for a limited number of servers

The Premium Version:

  • 350+ checks performed across the categories of Configuration, Reliability, Performance, Security, Server Info, Table/Index Design
  • New checks are constantly being added
  • Reminder list of recommendations that have been made previously and not yet fixed
  • List of issues fixed compared to the last collection
  • Can choose how long to store collected metadata, so that point in time reports can be made, along with automated estimates of DB growth over time
  • Can send 1 email per server or a single email for all servers
  • Ability to ‘mute’ recommendations on an individual basis, or entire check (for non-critical checks)
  • No practical limit on the number of servers

If you want to try it out, click this link to request a free access token.

Once you have an access token, here’s how to run it: How to run SQLFrontline