Tag - json

EXPLAIN FORMAT=JSON: cost_info knows why optimizer prefers one index to another

Percona Server 5.7 performance improvements

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 […]

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EXPLAIN FORMAT=JSON: buffer_result is not hidden!

MongoDB System Tuning

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

mysql> explain select * from salariesG
*************************** 1. row ***************************
[…]

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EXPLAIN FORMAT=JSON knows everything about UNIONs: union_result and query_specifications

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 of […]

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EXPLAIN FORMAT=JSON has details for subqueries in HAVING, nested selects and subqueries that update values

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 and

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