What are RDB and AOF

RDB：Redis DataBase, Writes a snapshot of a dataset in memory within a specified time interval ⼊ disk , The actual operation process is fork⼀ individual ⼦ process , First write the data set to ⼊ The temporary file , After writing successfully , Replace the previous ⽂ Pieces of , use ⼆ Binary compressed storage .

advantage ：

• Whole Redis The database will contain only ⼀ individual ⽂ Pieces of dump.rdb, Easy persistence .
• Good disaster tolerance , Easy backup .
• Maximize performance ,fork Sub process to complete the write operation , Let the main process continue processing commands , So it is IO Maximize . Use a single child process for persistence , The main process will not enter ⾏ whatever IO operation , To ensure the redis A high performance
• Relative to the dataset ⼤ when , Than AOF It's more efficient to start .

shortcoming ：

• Data security is low .RDB It's the interval ⼀ For a while ⾏ Persistence , If between persistence redis Hair ⽣ fault , Will send ⽣ Data loss . So this kind of ⽅ The formula is more suitable when the data requirements are not strict .
• because RDB It's through fork⼦ Process to assist in data persistence ⼯ Made , therefore , If the dataset is smaller ⼤ when , This may cause the entire server to stop ⽌ Service for hundreds of milliseconds , Even 1 Second .

AOF：Append Only File, Record every... Processed by the server in the form of a log ⼀ Write it 、 Delete operation , The query operation will not record , Record as text , Can open ⽂ See the detailed operation record

advantage ：

• Data security ,Redis Provided in 3 Medium synchronization policy , Synchronization per second 、 Sync and out of sync per change . in fact , Synchronization per second is also done asynchronously , It's also very efficient , The difference is ⼀ Once the system goes down , So this ⼀ Data modified within seconds will be lost . And every modification is synchronized , We can think of it as synchronous persistence , That is, every time ⽣ All data changes will be immediately recorded on disk .
• adopt append Pattern writing ⽂ Pieces of , Even if the server goes down halfway, it will not destroy the existing content , Can pass redis check-aof Tools to solve data ⼀ A sexual question .
• AOF The mechanism rewrite Pattern . On a regular basis AOF⽂ Piece to rewrite , In order to achieve the purpose of compression

shortcoming ：

• AOF File than RDB The file is big , And the recovery speed is slow .
• When the data set is large , Than rdb Low starting efficiency .
• Operational efficiency is not RDB high , AOF⽂ Piece ratio RDB High update frequency , priority of use AOF Restore data ,AOF Than RDB Safer and bigger ,RDB Performance ratio AOF good , If both have priority loading AOF.