Mempool syncing optimizations & fixups #89
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Overall this MR seems to greatly improve the initial sync and steady state of electrs alongside a slower bitcoind. some issues found during testing
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While tracing this with wireshark, I observed that electrs sends a request (such as getbestblockhash), and waits for a response. After 30 seconds (and a few TCP Keep-Alive interactions), bitcoind sends a FIN,ACK without any text response. Seems to be some behaviour in bitcoind. |
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I was unable to reproduce this, the "missing transaction" message appears to be returned as a JSONRPC error without panicking:
I'm seeing that behaviour on my local regtest env too. |
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utACK a6c181e |
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in analyzing pcap trace between local electrs and local. bitcoin rpc, we see electrs asking for getrawmempool on |
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2 issues
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following one of the "disconnects":
electrs should be responding to the FIN,ACK and active, and reopen
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RCasatta
dismissed
their stale review
I misread the comment about the disconnects
This should already be the case. In fact only errors explicitly constructed as an
Looking into this. |
bitcoind appears to close the connection after a period of inactivity, which can be adjusted with the (hidden) config option Adjusting it upwards made the disconnection issues I was experiencing in my local env go away. I also tested with electrs and bitcoind connected over the internet (local electrs connecting to a regtest bitcoind on a vps) and was able to retain open TCP connections with no disconnections for several hours (used every ~2 minutes, with I also tried investigating what's causing electrs not to close immediately in reply to bitcoind's FIN, but do not have an answer yet. |
This actually hurts performance because the batched response has to be bueffered on the bitcoind side, as @TheBlueMatt explains at romanz#373 (comment) Instead, send multiple individual RPC requests in parallel using a thread pool, with a separate RPC TCP connection for each thread. Also see romanz#374
The indexing process was adding transactions into the store so that prevouts funded & spent within the same batch could be looked up via Mempool::lookup_txos(). If the indexing process later failed for any reason, these transactions would remain in the store. With this change, we instead explicitly look for prevouts funded within the same batch, then look for the rest in the chain/mempool indexes and fail if any are missing, without keeping the transactions in the store.
Previously, if any of the mempool transactions were not available because they were evicted between getting the mempool txids and txs themselves, the mempool syncing operation would be aborted and tried again from scratch. With this change, we instead keep whatever transactions we were able to fetch, then get the updated list of mempool txids and re-try fetching missing ones continuously until we're able to get a full snapshot.
- Reduce logging level for bitcoind's JSONRPC response errors These can happen pretty often for missing mempool txs and do not warrant warn-level logging. Unexpected RPC errors will bubble up and be handled appropriately. - Add more verbose logging for mempool syncing
Keep RPC TCP connections open between sync runs and reuse them, to reduce TCP connection initialization overhead.
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Rebased and added some more verbose logging for mempool syncing. |
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testing latest commit using local electrs and bitcoind, I set parameters in bitcoin.conf I have not seen any "disconnected from daemon while receiving" messages. |
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utACK 5b07357 |
Optimizations:
Send RPC requests in parallel over multiple TCP connections, without batching (38e73d9)
The number of parallel requests to send can be controlled with a new
--daemon-parallelismCLI options (defaults to 4).Continuously attempt to fetch a full mempool snapshot, keeping whatever transactions we were able to get each time (6a14f40)
Fixups (not strictly necessary for the other changes, but touches on related areas and the previous behavior was wrong):
Don't add transactions with unknown parents to ensure mempool consistency (c60207a)
Make sure the chain tip doesn't move while fetching the mempool (a6a796c)
This will require adjusting bitcoind's
rpcthreadsand possiblyrpcworkqueueconfiguration options upwards. The defaultrpcthreadsis 4, which would be exhausted by mempool fetching alone (electrskeeps at least one other open connection, and we probably want to allow some room for other clients too).Based on top of #76. (now merged)