Currently the mempool isn't persisted across restarts. The historical argument against doing this is that it would make transactions immortal. Expiration now addresses that issue.

Without preserving the mempool node behavior changes drastically across restarts which complicates production use (e.g. mining overly small/low fee blocks) as well as development testing. The lack of retention also causes the loss of txn priority modifications made with prioritisetransaction which makes the API less reliable.

bool PreciousBlock(CValidationState& state, const CChainParams& params, CBlockIndex *pindex);
bool InvalidateBlock(CValidationState& state, const CChainParams& chainparams, CBlockIndex *pindex);
bool ResetBlockFailureFlags(CBlockIndex *pindex);
extern CChain chainActive;
extern CCoinsViewCache *pcoinsTip;
extern CBlockTreeDB *pblocktree;
/**
 * Return the spend height, which is one more than the inputs.GetBestBlock().
 * While checking, GetBestBlock() refers to the parent block. (protected by cs_main)
 * This is also true for mempool checks.
 */
int GetSpendHeight(const CCoinsViewCache& inputs);
extern VersionBitsCache versionbitscache;
/**
 * Determine what nVersion a new block should use.
 */
int32_t ComputeBlockVersion(const CBlockIndex* pindexPrev, const Consensus::Params& params);
/** Reject codes greater or equal to this can be returned by AcceptToMemPool
 * for transactions, to signal internal conditions. They cannot and should not
 * be sent over the P2P network.
 */
static const unsigned int REJECT_INTERNAL = 0x100;
static const unsigned int REJECT_HIGHFEE = 0x100;
static const unsigned int REJECT_ALREADY_KNOWN = 0x101;
static const unsigned int REJECT_CONFLICT = 0x102;
void DumpMempool();
bool LoadMempool();
void RegisterNodeSignals(CNodeSignals& nodeSignals);
void UnregisterNodeSignals(CNodeSignals& nodeSignals);
class PeerLogicValidation : public CValidationInterface {