When a Bitcoin transaction is made, it is stored in a Bitcoin node's mempool before it is confirmed into a block. When the rate of incoming transactions exceeds the rate transactions are confirmed, the mempool grows in size.
By default, Bitcoin Core allocates 300MB of memory for its mempool, so when a node's mempool grows big enough to use all 300MB of allocated memory, we say it's "full".
Once a node's mempool is using all of its allocated memory, it will start rejecting new transactions below a certain feerate threshold—so when this is the case, be extra sure to set a feerate that (at a minimum) exceeds that threshold. The current threshold feerate (and memory usage) are displayed right on Mempool's front page.
-mempool.space uses multiple Bitcoin nodes to obtain data: some with the default 300MB mempool memory limit (call these Small Nodes) and others with a much larger mempool memory limit (call these Big Nodes).
Many nodes on the Bitcoin network are configured to run with the default 300MB mempool memory setting. When all 300MB of memory are used up, such nodes will reject transactions below a certain threshold feerate. Running Small Nodes allows mempool.space to tell you what this threshold feerate is—this is the "Purging" feerate that shows on the front page when mempools are full, which you can use to be reasonably sure that your transaction will be widely propagated.
Big Node mempools are so big that they don't need to reject (or purge) transactions. Such nodes allow for mempool.space to provide you with information on any pending transaction it has received—no matter how congested the mempool is, and no matter how low-feerate or low-priority the transaction is.
From ef09912d1bc17c6256f81e4fa1eee7a801364d89 Mon Sep 17 00:00:00 2001 From: Mononaut