Replication basics in MySQL - Step-by-Step Execution

Concept Flow - Replication basics

Master writes data

↓

Binary log records changes

↓

Slave reads binary log

↓

Slave applies changes

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Slave data matches Master

Data changes on the master are recorded in a binary log, which the slave reads and applies to keep data synchronized.

Execution Sample

MySQL

CHANGE MASTER TO MASTER_LOG_FILE='mysql-bin.000001', MASTER_LOG_POS=154;
START SLAVE;
SHOW SLAVE STATUS\G;

This code sets the slave to start replication from a specific log file and position, then starts the slave and shows its status.

Execution Table

Step	Action	Master State	Slave State	Result
1	Master inserts row into table	Row added	No change	Master data updated
2	Master writes change to binary log	Binary log updated	No change	Change recorded
3	Slave reads binary log event	Binary log unchanged	Event read	Slave ready to apply
4	Slave applies event to its data	No change	Row added	Slave data updated
5	Slave sends acknowledgment	No change	Acknowledged	Replication confirmed
6	Check slave status	No change	Slave running, no errors	Replication active

💡 Replication continues as long as master writes and slave reads without errors

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	Final
Master Data	Empty	Row added	Row added	Row added	Row added	Row added	Row added
Binary Log	Empty	Empty	Change recorded	Change recorded	Change recorded	Change recorded	Change recorded
Slave Data	Empty	Empty	Empty	Event read	Row added	Row added	Row added
Slave Status	Stopped	Stopped	Stopped	Stopped	Running	Running	Running

Key Moments - 2 Insights

Why doesn't the slave data change immediately when the master inserts a row?

Because the slave first reads the change from the master's binary log (Step 3) before applying it (Step 4), as shown in the execution_table.

What happens if the slave cannot read the binary log?

The slave will stop applying changes and replication will pause, indicated by 'Slave Status' not changing to 'Running' in the variable_tracker.

Visual Quiz - 3 Questions

Look at the execution_table, at which step does the slave apply the master's data change?

A Step 3

B Step 4

C Step 2

D Step 5

💡 Hint

Check the 'Slave State' column in execution_table rows for when 'Row added' appears.

According to variable_tracker, what is the slave status after Step 4?

A Running

B Stopped

C Error

D Paused

💡 Hint

Look at the 'Slave Status' row and the value under 'After Step 4'.

If the master stops writing changes, what happens to the slave's binary log reading step?

A Slave continues reading new events

B Slave deletes its data

C Slave reads no new events and waits

D Slave restarts replication automatically

💡 Hint

Refer to the concept_flow where slave reads master's binary log to get changes.

Concept Snapshot

Replication basics in MySQL:
- Master records changes in binary log
- Slave reads binary log events
- Slave applies changes to its data
- Replication keeps slave data synchronized
- Use START SLAVE and SHOW SLAVE STATUS to manage

Full Transcript

Replication in MySQL works by the master server recording all data changes in a binary log. The slave server reads this binary log and applies the changes to its own data, keeping both databases synchronized. The process involves the master writing data, logging it, the slave reading the log, applying changes, and confirming replication status. Commands like CHANGE MASTER TO, START SLAVE, and SHOW SLAVE STATUS help control and monitor replication. This step-by-step flow ensures data consistency between master and slave servers.