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Stop caching every mempool tx for bitcoind - #1216
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ajaysehwal
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Nov 2, 2026
ajaysehwal
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Nov 2, 2026
With a bitcoind chain source, every mempool transaction was fetched into `mempool_txs_cache` and kept there until it left the mempool, so the node held a decoded copy of every transaction in bitcoind's mempool, which can reach hundreds of MB when the mempool is full. Only the onchain wallet consumes these transactions, and it keeps just the relevant ones. The cache only needs the transactions we may still have to emit, i.e., those that entered the mempool above our best processed height, and those a poll fetched before it failed, so the retry can resume where it left off. Restrict it to those, and shrink it after pruning. This only lowers steady-state memory use. `mempool_entries_cache` still holds one small entry per mempool transaction, and the first poll after startup still holds the whole mempool twice, in the cache and in the transactions it hands to the wallet, until the next poll prunes the cache. Also stop pre-sizing the transaction cache and the emit buffer to the whole mempool on every poll. This change was made with the help of Claude Code.
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Ldk-server was taking a lot of memory on my server. Doing this reduced memory by 100MB for me
With a bitcoind chain source, every mempool transaction was fetched into
mempool_txs_cacheand kept there until it left the mempool, so the node held a full decoded copy of bitcoind's mempool (roughly 0.9 KB per transaction, i.e. hundreds of MB when the mempool is full). Only the onchain wallet consumes these transactions, and it keeps just the relevant ones.The cache only serves transactions we may have to emit again, i.e. those that entered the mempool above our best processed height. Restrict it to those. Also stop shrinking the entries map and pre-sizing the emit buffer to the full mempool on every two-second poll, which churned multi-megabyte allocations and fragmented the heap.