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mempool: Optimize orphan map limiting. #1117

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merged 2 commits into from
Mar 4, 2018
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mempool: Optimize orphan map limiting. #1117

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0e71867
mempool: Optimize orphan map limiting.
davecgh Oct 24, 2016
2c14694
mempool: Optimize orphan map limiting.
dnldd Mar 3, 2018
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47 changes: 17 additions & 30 deletions mempool/mempool.go
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Original file line number Diff line number Diff line change
Expand Up @@ -7,10 +7,8 @@ package mempool

import (
"container/list"
"crypto/rand"
"fmt"
"math"
"math/big"
"sync"
"sync/atomic"
"time"
Expand Down Expand Up @@ -350,35 +348,19 @@ func (mp *TxPool) RemoveOrphan(txHash *chainhash.Hash) {
//
// This function MUST be called with the mempool lock held (for writes).
func (mp *TxPool) limitNumOrphans() error {
if len(mp.orphans)+1 > mp.cfg.Policy.MaxOrphanTxs &&
mp.cfg.Policy.MaxOrphanTxs > 0 {

// Generate a cryptographically random hash.
randHashBytes := make([]byte, chainhash.HashSize)
_, err := rand.Read(randHashBytes)
if err != nil {
return err
}
randHashNum := new(big.Int).SetBytes(randHashBytes)

// Try to find the first entry that is greater than the random
// hash. Use the first entry (which is already pseudorandom due
// to Go's range statement over maps) as a fallback if none of
// the hashes in the orphan pool are larger than the random
// hash.
var foundHash *chainhash.Hash
for txHash := range mp.orphans {
if foundHash == nil {
foundHash = &txHash
}
txHashNum := blockchain.HashToBig(&txHash)
if txHashNum.Cmp(randHashNum) > 0 {
foundHash = &txHash
break
}
}
if len(mp.orphans)+1 <= mp.cfg.Policy.MaxOrphanTxs {
return nil
}

mp.removeOrphan(foundHash)
// Remove a random entry from the map. For most compilers, Go's
// range statement iterates starting at a random item although
// that is not 100% guaranteed by the spec. The iteration order
// is not important here because an adversary would have to be
// able to pull off preimage attacks on the hashing function in
// order to target eviction of specific entries anyways.
for txHash := range mp.orphans {
mp.removeOrphan(&txHash)
break
}

return nil
Expand All @@ -388,6 +370,11 @@ func (mp *TxPool) limitNumOrphans() error {
//
// This function MUST be called with the mempool lock held (for writes).
func (mp *TxPool) addOrphan(tx *dcrutil.Tx) {
// Nothing to do if no orphans are allowed.
if mp.cfg.Policy.MaxOrphanTxs <= 0 {
return
}

// Limit the number orphan transactions to prevent memory exhaustion. A
// random orphan is evicted to make room if needed.
mp.limitNumOrphans()
Expand Down