ethereum/go-ethereum · error

Trying to insert into existing key

Error message

Trying to insert into existing key

What it means

Error "Trying to insert into existing key" thrown in ethereum/go-ethereum.

Source

Thrown at trie/stacktrie.go:288

		// Insert both child leaves where they belong:
		origIdx := st.key[diffidx]
		newIdx := key[diffidx]
		p.children[origIdx] = n
		p.children[newIdx] = o
		st.key = st.key[:diffidx]

	case leafNode: /* Leaf */
		// Compare both key chunks and see where they differ
		diffidx := st.getDiffIndex(key)

		// Overwriting a key isn't supported, which means that
		// the current leaf is expected to be split into 1) an
		// optional extension for the common prefix of these 2
		// keys, 2) a fullnode selecting the path on which the
		// keys differ, and 3) one leaf for the differentiated
		// component of each key.
		if diffidx >= len(st.key) {
			panic("Trying to insert into existing key")
		}

		// Check if the split occurs at the first nibble of the
		// chunk. In that case, no prefix extnode is necessary.
		// Otherwise, create that
		var p *stNode
		if diffidx == 0 {
			// Convert current leaf into a branch
			st.typ = branchNode
			st.children[0] = nil
			p = st
		} else {
			// Convert current node into an ext,
			// and insert a child branch node.
			st.typ = extNode
			st.children[0] = stPool.Get().(*stNode)
			st.children[0].typ = branchNode
			p = st.children[0]

View on GitHub (pinned to 6bb0588ad8)

Solutions

1. StackTrie does not support overwriting an existing key. Ensure keys are inserted exactly once and in strictly increasing (sorted) order.
2. If updates are needed, collect all key/value pairs first and build the StackTrie once from the final set.

Example fix

sort.Slice(kvs, func(i, j int) bool { return bytes.Compare(kvs[i].K, kvs[j].K) < 0 })
for _, kv := range kvs {
    st.Update(kv.K, kv.V) // each key exactly once, ascending order
}

When it happens

Trigger: Calling StackTrie.Update/insert with a key that already exists in the trie, or with unsorted input keys.

Common situations: Building a stacktrie from duplicate or unsorted key/value lists (e.g., receipts/tx lists containing duplicates).

AI-assisted analysis of ethereum/go-ethereum@6bb0588ad8 (2026-08-15). Data as JSON: /api/errors/b509d490a121362f. Report an issue: GitHub.