Overview

We want

• Transactions
• (Our own) priority for these transactions

to be persistent across restarts, crashes and power outages.

These two functions do that for us:

• DumpMempool() writes mempool and transaction priority to mempool.dat
• LoadMempool() reads mempool and transaction priority from mempool.dat

The mempool.dat file is located in the bitcoin -datadir.

Manually prioritizing transactions

bitcoin-cli getmempoolentry 5783dd3f...

{

"fees": {

"base": 0.00080000,

"modified": 0.00080000,

"ancestor": 0.00080000,

"descendant": 0.00080000

},

"vsize": 707,

"fee": 0.00080000,

"modifiedfee": 0.00080000,

...

}

bitcoin-cli getmempoolentry 5783dd3f...

{

"fees": {

"base": 0.00080000,

"modified": 0.00090000,

"ancestor": 0.00090000,

"descendant": 0.00090000

},

"vsize": 707,

"fee": 0.00080000,

"modifiedfee": 0.00090000,

…

}

​

bitcoin-cli prioritisetransaction 5783dd3f... 0 10000

mempool.dat file structure

​

struct File{

Header header; // information about the file

vector<Entry> entries; // mempool entries

map<uint256, CAmount> mapDeltas; // tx prioritization

}

struct Header {

uint64_t version; // file version

uint64_t entryCount; // transaction count in file

};

struct Entry {

CTransaction tx; // raw tx

int64_t nTime; // mempool entry time

int64_t nFeeDelta; // tx prioritization

};

LoadMempool() in validation.cpp

1. Open the mempool.dat to read from
2. Read the file header (version and entryCount)
3. Check header.version == MEMPOOL_DUMP_VERSION // currently 1 .
4. Read entries (for the number of entries specified by header.entryCount)
1. Prioritize the transaction (if prioritization data exist)
2. (Try to) accept the transaction to the mempool
3. Count valid, invalid, expired and already-there transactions
5. Read extra transaction prioritization data from mapDeltas
6. Print transaction import statistics

LoadMempool() is called in the import thread (after loading/reindexing/activation of blocks)

​

Imported mempool transactions from disk: 463 succeeded, 10 failed, 0 expired, 0 already there..

Current behavior of mempool persisting

Persisting to mempool.dat added in PR #8448 and first included in Bitcoin Core v0.14.0

• LoadMempool() is executed after after loading/reindexing/activation of blocks
• In background (getmempoolinfo returns ”loaded”: true when loaded)
• No real problem if file is not loadable
• Log message: statistics about the validity of the processed transactions
• DumpMempool() is executed at shutdown
• No real problem if file is not writeable
• Log message: time taken to dump the transactions

Can be manually disabled with -persistmempool=0 introduced in PR #9966 (v0.15.0)

Manually save to mempool.dat with the savemempool RPC introduced in PR #11099 (v.0.16.0)

​

Thank you and questions?

​

PrioritiseTransaction: 0000000000000000001ef7e2989941f6fba4a9bbae418de42e26e413b36a53ab feerate += 0.19999998

​

Imported mempool transactions from disk: 2199 succeeded, 0 failed, 0 expired, 0 already there

​

​

My debug.log at startup

Not a transaction