Embed silently fails on append
Author: dainiusjocasCreated Aug 19, 2026Updated Aug 26, 2026
Describe the bug As of 8.738.17, when a partial update appends to an array field and an embedding is calculated from that field, the synthetic tensor field is silently not updated.
To Reproduce Steps to reproduce the behavior:
- Here is the full application.
- Schema
schema doc {
document doc {
struct chunk {
field text type string {}
field sentiment type int {}
}
field chunks type array<chunk> {
indexing: summary
}
}
# Simply take a value from the document field which was fed and embed it.
# truncated to just 1 dense dimension for simplicity
field embeddings type tensor<float>(offset{}, x[1]) {
indexing {
input chunks |
for_each{ get_field text } |
embed e5 |
attribute
}
attribute {
distance-metric: angular
}
}
field text type array<string> {
indexing: input chunks | for_each{ get_field text } | index
}
}- Upsert a doc:
curl -v -X PUT -H "Content-Type:application/json" --data '
{
"create": true,
"update": "id:doc:doc::1",
"fields": {
"chunks": {
"add": [
{"text": "three", "sentiment": 20}
]
}
}
}' \
http://localhost:8080/document/v1/doc/doc/docid/1- See the doc contents:
vespa visit --field-set="[all]" | jqReturns:
{
"id": "id:doc:doc::1",
"fields": {
"chunks": [
{
"text": "three",
"sentiment": 20
}
],
"text": [
"three"
]
}
}See that embeddings field is not returned.
While after a regular PUT, all embeddings are calculated.
Expected behavior Something along the lines:
- maybe a note in the documentation.
- feed response could signal that something was not updated, maybe a custom header
- embedder could have a mode where tensor labels are made as a hash from the content. But a tough problem.
Environment (please complete the following information):
- OS: MacOS, docker
- Infrastructure: self-hosted
Vespa version 8.738.17
Additional context Demo.
Source: vespa-engine/vespa