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@@ -2088,24 +2088,26 @@
<p><strong>Prerequisites</strong></p>
<p>Install Docker</p>
<p><strong>Setup</strong></p>
<p>Create a working directory named sos or something similar, and cd into it.</p>
<p>Enter the following into a file named my.cnf under a directory named custom.</p>
<pre><code>sos $ cat custom/my.cnf
<p>Create a working directory named <code>sos</code> or something similar, and <code>cd</code> into it.</p>
<p>Enter the following into a file named <code>my.cnf</code> under a directory named <code>custom</code>:</p>
<pre><code class="language-shell">sos $ cat custom/my.cnf
[mysqld]
# These settings apply to MySQL server
# You can set port, socket path, buffer size etc.
# Below, we are configuring slow query settings
slow_query_log=1
slow_query_log_file=/var/log/mysqlslow.log
long_query_time=1
</code></pre>
<p>Start a container and enable slow query log with the following:</p>
<pre><code>sos $ docker run --name db -v custom:/etc/mysql/conf.d -e MYSQL_ROOT_PASSWORD=realsecret -d mysql:8
<pre><code class="language-shell">sos $ docker run --name db -v custom:/etc/mysql/conf.d -e MYSQL_ROOT_PASSWORD=realsecret -d mysql:8
sos $ docker cp custom/my.cnf $(docker ps -qf &quot;name=db&quot;):/etc/mysql/conf.d/custom.cnf
sos $ docker restart $(docker ps -qf &quot;name=db&quot;)
</code></pre>
<p>Import a sample database</p>
<pre><code>sos $ git clone git@github.com:datacharmer/test_db.git
<p>Import a sample database:</p>
<pre><code class="language-shell">sos $ git clone git@github.com:datacharmer/test_db.git
sos $ docker cp test_db $(docker ps -qf &quot;name=db&quot;):/home/test_db/
sos $ docker exec -it $(docker ps -qf &quot;name=db&quot;) bash
root@3ab5b18b0c7d:/# cd /home/test_db/
@@ -2113,15 +2115,15 @@ root@3ab5b18b0c7d:/# mysql -uroot -prealsecret mysql &lt; employees.sql
root@3ab5b18b0c7d:/etc# touch /var/log/mysqlslow.log
root@3ab5b18b0c7d:/etc# chown mysql:mysql /var/log/mysqlslow.log
</code></pre>
<p><em>Workshop 1: Run some sample queries</em>
Run the following</p>
<pre><code>$ mysql -uroot -prealsecret mysql
<p><em>Workshop 1: Run some sample queries</em></p>
<p>Run the following:</p>
<pre><code class="language-shell">$ mysql -uroot -prealsecret mysql
mysql&gt;
# inspect DBs and tables
# the last 4 are MySQL internal DBs
mysql&gt; show databases;
mysql&gt; SHOW DATABASES;
+--------------------+
| Database |
+--------------------+
@@ -2132,8 +2134,8 @@ mysql&gt; show databases;
| sys |
+--------------------+
&gt; use employees;
mysql&gt; show tables;
mysql&gt; USE employees;
mysql&gt; SHOW TABLES;
+----------------------+
| Tables_in_employees |
+----------------------+
@@ -2148,18 +2150,19 @@ mysql&gt; show tables;
+----------------------+
# read a few rows
mysql&gt; select * from employees limit 5;
mysql&gt; SELECT * FROM employees LIMIT 5;
# filter data by conditions
mysql&gt; select count(*) from employees where gender = 'M' limit 5;
mysql&gt; SELECT COUNT(*) FROM employees WHERE gender = 'M' LIMIT 5;
# find count of particular data
mysql&gt; select count(*) from employees where first_name = 'Sachin';
mysql&gt; SELECT COUNT(*) FROM employees WHERE first_name = 'Sachin';
</code></pre>
<p><em>Workshop 2: Use explain and explain analyze to profile a query, identify and add indexes required for improving performance</em></p>
<pre><code># View all indexes on table
#(\G is to output horizontally, replace it with a ; to get table output)
mysql&gt; show index from employees from employees\G
<pre><code class="language-shell"># View all indexes on table
# (\G is to output horizontally, replace it with a ; to get table output)
mysql&gt; SHOW INDEX FROM employees FROM employees\G
*************************** 1. row ***************************
Table: employees
Non_unique: 0
@@ -2177,10 +2180,11 @@ Index_comment:
Visible: YES
Expression: NULL
# This query uses an index, idenitfied by 'key' field
# This query uses an index, identified by 'key' field
# By prefixing explain keyword to the command,
# we get query plan (including key used)
mysql&gt; explain select * from employees where emp_no &lt; 10005\G
mysql&gt; EXPLAIN SELECT * FROM employees WHERE emp_no &lt; 10005\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
@@ -2196,7 +2200,8 @@ possible_keys: PRIMARY
Extra: Using where
# Compare that to the next query which does not utilize any index
mysql&gt; explain select first_name, last_name from employees where first_name = 'Sachin'\G
mysql&gt; EXPLAIN SELECT first_name, last_name FROM employees WHERE first_name = 'Sachin'\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
@@ -2212,20 +2217,22 @@ possible_keys: NULL
Extra: Using where
# Let's see how much time this query takes
mysql&gt; explain analyze select first_name, last_name from employees where first_name = 'Sachin'\G
mysql&gt; EXPLAIN ANALYZE SELECT first_name, last_name FROM employees WHERE first_name = 'Sachin'\G
*************************** 1. row ***************************
EXPLAIN: -&gt; Filter: (employees.first_name = 'Sachin') (cost=30143.55 rows=29911) (actual time=28.284..3952.428 rows=232 loops=1)
-&gt; Table scan on employees (cost=30143.55 rows=299113) (actual time=0.095..1996.092 rows=300024 loops=1)
# Cost(estimated by query planner) is 30143.55
# Cost (estimated by query planner) is 30143.55
# actual time=28.284ms for first row, 3952.428 for all rows
# Now lets try adding an index and running the query again
mysql&gt; create index idx_firstname on employees(first_name);
mysql&gt; CREATE INDEX idx_firstname ON employees(first_name);
Query OK, 0 rows affected (1.25 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql&gt; explain analyze select first_name, last_name from employees where first_name = 'Sachin';
mysql&gt; EXPLAIN ANALYZE SELECT first_name, last_name FROM employees WHERE first_name = 'Sachin';
+--------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+--------------------------------------------------------------------------------------------------------------------------------------------+
@@ -2237,24 +2244,28 @@ mysql&gt; explain analyze select first_name, last_name from employees where firs
# Actual time=0.551ms for first row
# 2.934ms for all rows. A huge improvement!
# Also notice that the query involves only an index lookup,
# and no table scan (reading all rows of table)
# ..which vastly reduces load on the DB.
# and no table scan (reading all rows of the table),
# which vastly reduces load on the DB.
</code></pre>
<p><em>Workshop 3: Identify slow queries on a MySQL server</em></p>
<pre><code># Run the command below in two terminal tabs to open two shells into the container.
docker exec -it $(docker ps -qf &quot;name=db&quot;) bash
<pre><code class="language-shell"># Run the command below in two terminal tabs to open two shells into the container.
# Open a mysql prompt in one of them and execute this command
$ docker exec -it $(docker ps -qf &quot;name=db&quot;) bash
# Open a `mysql` prompt in one of them and execute this command
# We have configured to log queries that take longer than 1s,
# so this sleep(3) will be logged
mysql -uroot -prealsecret mysql
# so this `sleep(3)` will be logged
$ mysql -uroot -prealsecret mysql
mysql&gt; select sleep(3);
# Now, in the other terminal, tail the slow log to find details about the query
root@62c92c89234d:/etc# tail -f /var/log/mysqlslow.log
/usr/sbin/mysqld, Version: 8.0.21 (MySQL Community Server - GPL). started with:
Tcp port: 3306 Unix socket: /var/run/mysqld/mysqld.sock
Time Id Command Argument
# Time: 2020-11-26T14:53:44.822348Z
# User@Host: root[root] @ localhost [] Id: 9
# Query_time: 5.404938 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 1
@@ -2262,6 +2273,7 @@ use employees;
# Time: 2020-11-26T14:53:58.015736Z
# User@Host: root[root] @ localhost [] Id: 9
# Query_time: 10.000225 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 1
SET timestamp=1606402428;
select sleep(3);
</code></pre>