Redis trend —NVM Memory

NVM What is it?

NVM Full name Non-Volatile Memory Nonvolatile storage ,NVM It is characterized by large capacity 、 Fast 、 Support persistent data , This feature and Redis The goals we pursue coincide , So in practice Redis You can put NVM As memory DRAM Use .

NVM Memory characteristics

NVM Memory and traditional DRAM What are the advantages of memory ？

• NVM Memory can directly persist data , Data saved in NVM After memory , Even in case of power failure or downtime , The data will still be stored in NVM In the memory , While traditional DRAM Memory power failure or downtime will lead to DRAM Memory data loss .

• NVM The access speed of memory is close to DRAM The speed of , Remember that this is near, not over ,NVM The memory read latency is about 200~300ns, Write delay approx 100ns.

• NVM The memory capacity is very large ,NVM The device density is very high , Single root NVM Memory modules can achieve 128G The maximum capacity can even reach 512G, So we can use NVM Memory is easy to build TB Level of memory .

NVM product AEP Memory

Now the industry has NVM Memory products ,Intel stay 2019 year 4 Month launch Optane AEP Memory module （ abbreviation AEP Memory ）,AEP Memory provides two usage modes for software , The partial emphasis of these two models is NVM Large capacity , Persistent save data .

• Memory Pattern , This model is to NVM Use it as a large memory , This mode does not enable persistence , Does that mean that Memory Patterns don't need DRAM Traditional memory ？ Not that the server still needs to be configured DRAM Memory , however DRAM Memory is treated as AEP Memory cache usage ,DRAM The memory space of is not visible to the application software , The application will use AEP Of memory space .

• APP Direct Pattern , This model will NVM Used as a persistent memory , That is, the application software writes the data to AEP On memory , The data is directly persisted , This is also called persistent memory （Persistent Memory abbreviation PM）.

Redis use AEP Advantages of memory

Redis If the AEP Memory as storage , So it needs to be considered in different modes

Memory Pattern

Redis use Memory Pattern is to use its large capacity to save a large amount of data ,Redis It can also provide large capacity storage for businesses ,Redis It can be like DRAM No code modification is required for memory operation .

But it should be noted that AEP Memory access latency is certainly higher than traditional DRAM High memory , because AEP It is NVM An implementation of ,NVM There are access and read-write delays , So we need to make a trade-off between read-write latency and large capacity .

APP Direct Pattern

Redis De application APP Direct After the model , So write AEP Memory data will be automatically persisted , There's no need to Redis Some persistence mechanisms of , Because no matter it is AOF still RDB Persistence mode , There is a risk of data loss , Moreover, persistence operation may cause some problems

• RDB Persistence ,fork The child process blocks the main thread .

• AOF File logging , There is a trade-off between reliability and write performance , It is generally recommended to choose a compromise everysec.

• AOF and RDB When a file recovers data , Recovery speed is affected by RDB Document and AOF File size limit .

So in APP Direct Mode can make full use of PM Characteristics of persistent memory , avoid Redis Some problems caused by self persistence .