5
What’s Different?
A wide variety of key-value libraries are available in practically every programming
language. The persistent memory example in Listing 1-1 is different because the keyvalue store itself resides in persistent memory. For comparison, Figure 1-1 shows how a
key-value store using traditional storage is laid out.
When the application in Figure 1-1 wants to fetch a value from the key-value store,
a buffer must be allocated in memory to hold the result. This is because the values are
kept on block storage, which cannot be addressed directly by the application. The only
way to access a value is to bring it into memory, and the only way to do that is to read
full blocks from the storage device, which can only be accessed via block I/O. Now
consider Figure 1-2, where the key-value store resides in persistent memory like our
sample code.
Figure 1-1. A key-value store on traditional storage
CHApter 1 IntroduCtIon to persIstent MeMory proGrAMMInG
What’s Different?
A wide variety of key-value libraries are available in practically every programming
language. The persistent memory example in Listing 1-1 is different because the keyvalue store itself resides in persistent memory. For comparison, Figure 1-1 shows how a
key-value store using traditional storage is laid out.
When the application in Figure 1-1 wants to fetch a value from the key-value store,
a buffer must be allocated in memory to hold the result. This is because the values are
kept on block storage, which cannot be addressed directly by the application. The only
way to access a value is to bring it into memory, and the only way to do that is to read
full blocks from the storage device, which can only be accessed via block I/O. Now
consider Figure 1-2, where the key-value store resides in persistent memory like our
sample code.
Figure 1-1. A key-value store on traditional storage
CHApter 1 IntroduCtIon to persIstent MeMory proGrAMMInG