Redis RDB snapshot

2 Commands to generate snapshots

save In the main thread , Will block the main thread
bgsave Create sub processes to execute snapshot tasks

Full snapshot

Take a snapshot of all data

Incremental snapshot

Make changes based on the last full snapshot
Suppose that t0 Take a full snapshot at any time
stay t1 The data change operation is carried out at any time
stay t2 To take a snapshot, you need to know t1 What did you do at any time
Doing incremental backup requires additional overhead to record data changes

Full snapshot + AOF

redis 4 In the future, it provides services like mysql Same snapshot + journal To recover data

Read / write processing of snapshots

hypothesis redis Large amount of data ,t0 moment data A = 10
t0 Take snapshots all the time , Snapshot time 10 minute , After the snapshot A It should be equal to 10
If the ninth minute will A Change to 9. How to ensure the results of snapshots A = 10
Give Way redis Write operations , Waiting for a snapshot is unrealistic
redis Solve this problem , Using the write time copy of the operating system
When taking a snapshot , The subprocess copies the necessary data of the memory of the main thread , And point to the same memory space , Share the same data .
When in the main thread redis When modifying data , Will reallocate a memory space （ copy ）, Copy the original data into a copy for the sub process to use