Does geth/parity nodes have a maximum limit of transactions that they can have (in queue) after which they stop accepting transactions (or apply back pressure or something)
Has a default queue size of 8192, but this can be controlled using the
--tx-queue-size command line option.
--tx-queue-size=[LIMIT] Maximum amount of transactions in the queue (waiting to be included in next block). (default: 8192)
Default global queue size of 1024, which is again configurable, with
--txpool.globalqueue. There are also options for per-account queue sizes.
--txpool.globalqueue value Maximum number of non-executable transaction slots for all accounts (default: 1024)
(See Transaction Pool Options of this page.)