The cache is a space in the random access memory used as temporary storage. In-memory cache refers to the data storage layer that’s in-between the programs and databases. They store data from earlier requests or data copied directly from the database.
On the other hand, in-memory databases are purpose-built databases that rely solely on memory for data storage. Most of them can persist the data stored on the disks by taking snapshots. Here are the differences between in-memory cache and in-memory databases.
Mode of operations
For the in-memory cache to work, it has to set aside some part of the random access memory that will function as the cache. Before an application reads data from the storage, it first checks if it is available in the cache memory. If the data is found, it’s read; if not, it is then read from the source.
That’s why it’s described as a cache with performance-critical information of the database shared across the available requests in a particular application. In this case, there is direct access to the memory rather through other mechanisms. And this enables all the related operations to work effectively throughout the process.
If data is not found in the cache memory, the data is retrieved from the source and then written on the in-memory cache so that it will be available next time. In the case of distributed cache, the cache memory is between the database and the application, depending on the deployment model. It’s distributed between the nodes and operates based on the distributed hash table and the retrieved type.
On the other hand, the in-memory database, also known as “main-memory,” has advanced data structures optimized for working with memory. It has direct pointers for managing the interrelationships between different parts of the database.
It makes data available all the time it’s needed. In this case, the data is not located on the computer system’s hard disks, hence eliminating the need for the input/output tasks.
In an in-memory database, the data must be inconsistent before and after the transaction. There is no other process that can change while the transaction is running.
The difference in terms of structure
In-memory cache is located on the processor itself, while the in-memory database is a part of the secondary storage. The cache memory location between the CPU and the main memory provides a quicker way for accessing data from the random-access memory.
Data is moved as a word transfer between the CPU and the cache and then transformed into blocks before transferring between the main memory and the cache. These blocks are generally known as pages. The in-memory cache is the essence of speed on both ends.
A multilevel cache is often used by businesses with large data sizes to be accessed. That’s because large data sizes tend to affect the cache processing speed. The in-memory cache structure is smaller than that of the in-memory database.
To be a success, the experts on the enterprise IT system have to organize different caches at multiple levels to improve the processing speed of the cache. Smaller caches tend to have greater speed and are often placed close to the CPU, while the large caches are away from the CPU. The in-memory cache structure makes it faster in operation than the in-memory database.
The difference in terms of cost
In-memory cache is very expensive compared to the in-memory database. That’s why only a little of it is used compared to the in-memory database. The more in-memory cache a computer has, the higher the processing speed.
It operates 10 to 100 times faster than the random-access memory; that’s just a few nanoseconds to respond to the CPU request. One common hardware used for the cache memory is the high-speed static random-access memory.
Types of cache memory
There are generally three levels of the cache, with the L1 cache being the primary cache that is usually embedded in the processor chip. The L2 cache is often designed to be more capacious than the L1.
It’s also embedded on the CPU or a separate coprocessor with a high-speed alternative system bus connecting it and the CPU. The communication links(bus) ensure that it doesn’t get slowed by the traffic on the main system bus.
L3 is a type of cache developed to improve the operational capability of the L1 and L3. Its speed doubles that of DRAM as it has multiple multiprocessors. The future of the cache memory seems to be consolidating all three levels of the memory caching on the central processing unit.
This has begun with the shift from acquiring a specific motherboard designed with different chipsets and buses to purchasing a CPU with just the correct amount of the integrated caches.
Types of main memory
The main memory can be divided into two major categories; RAM and ROM. RAM loses its contents when the power is switched off. Data and instructions are entered into the RAM from the external disk and then processed and taken back into the hard disk. This data is read directly using the memory addresses regardless of the length of the data.
The RAM also has two subcategories; the Static Random Access Memory (SRAM) and the Dynamic Random Access Memory (DRAM). For the SRAM, transistors are supplied with a constant power supply to make it alive.
The data remains static, and hence no refresh is needed. DRAM is mainly built with capacitors that gradually lose energy over time, which implies that data is likely to be lost. That calls for a periodic refresh to retain all the data.
ROM is a non-volatile memory that holds the contents even when the power is switched off. The contents of this memory can only be read and cannot be rewritten. These are contents like the boot program and firmware. ROM has two main subcategories; programmable ROM and the Erasable Programmable ROM. PROM is sold as a blank space device, while the EPROM can be erased and reprogrammed using an electrical signal.