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Showing entries 1 to 10 of 75 10 Older Entries

Displaying posts with tag: explain (reset)

Introduction to Troubleshooting Performance – Troubleshooting Slow Queries webinar: Q & A
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In this blog, I will provide answers to the Q & A for the Troubleshooting Slow Queries webinar.

First, I want to thank you for attending the April 28 webinar. The recording and slides for the webinar are available here. Below is the list of your questions that I wasn’t …

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EXPLAIN FORMAT=JSON wrap-up
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This blog is an EXPLAIN FORMAT=JSON wrap-up for the series of posts I’ve done in the last few months.

In this series, we’ve discussed everything unique to

EXPLAIN FORMAT=JSON

. I intentionally skipped a description of members such as

table_name

,

access_type

  or

select_id

, which are not unique.

In this series, I only mentioned in …

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EXPLAIN FORMAT=JSON: nested_loop makes JOIN hierarchy transparent
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Once again it’s time for another EXPLAIN FORMAT=JSON is cool! post. This post will discuss how EXPLAIN FORMAT=JSON allows the nested_loop command to make the JOIN operation hierarchy transparent.

The regular

EXPLAIN

  command lists each table that participates in a 

JOIN

  operation on a single row. …

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EXPLAIN FORMAT=JSON: cost_info knows why optimizer prefers one index to another
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Time for another entry in the EXPLAIN FORMAT=JSON is cool! series of blog posts. This time we’ll discuss how using EXPLAIN FORMAT=JSON allows you to see that

cost_info

  knows why the optimizer prefers one index to another.

Tables often have more than one index. Any of these indexes can be used to resolve query. The optimizer has to …

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EXPLAIN FORMAT=JSON: buffer_result is not hidden!
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Time for another entry in the EXPLAIN FORMAT=JSON is cool! series. Today we’re going to look at how you can view the buffer result using JSON (instead of the regular

EXPLAIN

 command.

Regular

EXPLAIN

 does not identify if

SQL_BUFFER_RESULT

 was used at all. To demonstrate, let’s run this query:

mysql> explain …
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EXPLAIN FORMAT=JSON knows everything about UNIONs: union_result and query_specifications
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Ready for another post in the EXPLAIN FORMAT=JSON is Cool series! Great! This post will discuss how to see all the information that is contained in optimized queries with

UNION

 using the

union_result

 and

query_specifications

 commands.

 

When optimizing complicated queries with

UNION

, it is easy to get lost in the regular

EXPLAIN

  output trying to identify which part …

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EXPLAIN FORMAT=JSON has details for subqueries in HAVING, nested selects and subqueries that update values
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Over several previous blog posts, we’ve already discussed what information the 

EXPLAIN FORMAT=JSON

 output provides for some subqueries. You can review those discussions here, here

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ordering_operation: EXPLAIN FORMAT=JSON knows everything about ORDER BY processing
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We’ve already discussed using the ORDER BY clause with subqueries. You can also, however, use the 

ORDER BY

 clause with sorting results of one of the columns. Actually, this is most common way to use this clause.

Sometimes such queries require using temporary tables or filesort, and a regular

EXPLAIN

  clause provides this information. But it …

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grouping_operation, duplicates_removal: EXPLAIN FORMAT=JSON has all details about GROUP BY
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In the previous EXPLAIN FORMAT=JSON is Cool! series blog post, we discussed the  

group_by_subqueries

  member (which is child of

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EXPLAIN FORMAT=JSON: order_by_subqueries, group_by_subqueries details on subqueries in ORDER BY and GROUP BY
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Another post in the EXPLAIN FORMAT=JSON is Cool! series! In this post, we’ll discuss how the EXPLAIN FORMAT=JSON provides optimization details for 

ORDER BY

 and  

GROUP BY

 operations in conjunction with 

order_by_subqueries

 and   …

  [Read more...]
Showing entries 1 to 10 of 75 10 Older Entries

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