The BitCoin Mempool is the storage area for all pending BitCoin transactions. Here's how it works. When you perform a transaction, it is first transmitted and verified by the available BitCoin nodes. Upon verification completion, it then goes into the Mempool (Memory Pool). The transaction waits in the pool until the next available BitCoin miner processes it into the next available BitCoin block.
Every node has a different rendition of the transactions waiting to be processed due to the fact that these nodes have different RAM storage capacities. This also explains the different numbers of transactions found within each pool.
Due to the limited RAM available for each pool, the node allocates transactions according to their size by applying a minimal fee threshold. Transactions with fees per kB that are lower than the threshold are instantly removed from the Mempool and only new transactions with a fee per kB large enough are given access to the Mempool.
Also whenever a node gets a new valid block of transactions, it removes and processes all the transactions contained within that block from its Mempool. The Mempool size will of course sharply decrease in preparation for a new block of transactions.
The BitCoin Mempool and Bitcoin Improvement Proposals.
Bitcoin Improvement Proposals (BIPs) are the design documents created for introducing features or information to the Bitcoin protocol. These proposals are the standard way of conveying ideas since Bitcoin, being open-source, has no formal structure.
The BitCoin Mempool is a part of the BIP 35 Bitcoin Improvement Proposal. The proposal can be easily found on the Github website. This technology also helps SPV wallets (lightweight client wallets) record and maintain transactions across the network.
The BitCoin Mempool and Simplified Payment Verification.
SPV wallets play a very important role in BitCoin transactions. SPV is the acronym for "Simplified Payment Verification". This is a Bitcoin protocol feature that is usually implemented in client wallets. It allows the creation of "lightweight" bitcoin wallet clients.
These types of wallets that do not need to download the entire BitCoin BlockChain in order to work. This makes it possible to install an SPV wallet onto your mobile phones, tablet or any other device that has limited space.
The BitCoin Mempool vs Transaction Speed.
The overall speed of processing transactions over the network is determined by the rate of mining new blocks of transactions verses the rate of new transactions arriving into the Mempool.
If the rate of mining new blocks of transactions ever becomes lower than the rate of new transactions arriving into the Mempool, then you will have what is considered a "bottleneck" situation. In this scenario, transactions can take a longer time to get approved. This is of course dependent on the transaction size and the attached fee.
BitCoin Mempool Analysis.
For a visual analysis (filled with real-time charts) of the BitCoin Mempool, you can go to the BitCoin Ticker website (bitcointicker.co/networkstats/). This is one of the places where you can go to analyze the overall health of the BitCoin network.
In the charts, you can view the current Mempool size, the number of node connections, the speed of transactions, the total number of BitCoins processed and the latest transactions. Understanding the statistical data displayed is important to anyone who is interested in the world of BitCoins.
BitCoins are still (relatively speaking) in the infancy stage. As technology improves, these advancements will improve the BitCoin infrastructure which will lead to even faster transactions across the BitCoin Mempool. At this current rate, there will soon come a time when BitCoin transactions can be verified almost instantly from anywhere in the world.