PartialResultSet

Partial results from a streaming read or SQL query. Streaming reads and SQL queries better tolerate large result sets, large rows, and large values, but are a little trickier to consume.

JSON representation
{
  "metadata": {
    object(ResultSetMetadata)
  },
  "values": [
    value
  ],
  "chunkedValue": boolean,
  "resumeToken": string,
  "stats": {
    object(ResultSetStats)
  }
}
Fields
metadata

object(ResultSetMetadata)

Metadata about the result set, such as row type information. Only present in the first response.

values[]

value (Value format)

A streamed result set consists of a stream of values, which might be split into many PartialResultSet messages to accommodate large rows and/or large values. Every N complete values defines a row, where N is equal to the number of entries in metadata.row_type.fields.

Most values are encoded based on type as described here.

It is possible that the last value in values is "chunked", meaning that the rest of the value is sent in subsequent PartialResultSet(s). This is denoted by the chunkedValue field. Two or more chunked values can be merged to form a complete value as follows:

  • bool/number/null: cannot be chunked
  • string: concatenate the strings
  • list: concatenate the lists. If the last element in a list is a string, list, or object, merge it with the first element in the next list by applying these rules recursively.
  • object: concatenate the (field name, field value) pairs. If a field name is duplicated, then apply these rules recursively to merge the field values.

Some examples of merging:

# Strings are concatenated.
"foo", "bar" => "foobar"

# Lists of non-strings are concatenated.
[2, 3], [4] => [2, 3, 4]

# Lists are concatenated, but the last and first elements are merged
# because they are strings.
["a", "b"], ["c", "d"] => ["a", "bc", "d"]

# Lists are concatenated, but the last and first elements are merged
# because they are lists. Recursively, the last and first elements
# of the inner lists are merged because they are strings.
["a", ["b", "c"]], [["d"], "e"] => ["a", ["b", "cd"], "e"]

# Non-overlapping object fields are combined.
{"a": "1"}, {"b": "2"} => {"a": "1", "b": 2"}

# Overlapping object fields are merged.
{"a": "1"}, {"a": "2"} => {"a": "12"}

# Examples of merging objects containing lists of strings.
{"a": ["1"]}, {"a": ["2"]} => {"a": ["12"]}

For a more complete example, suppose a streaming SQL query is yielding a result set whose rows contain a single string field. The following PartialResultSets might be yielded:

{
  "metadata": { ... }
  "values": ["Hello", "W"]
  "chunkedValue": true
  "resumeToken": "Af65..."
}
{
  "values": ["orl"]
  "chunkedValue": true
  "resumeToken": "Bqp2..."
}
{
  "values": ["d"]
  "resumeToken": "Zx1B..."
}

This sequence of PartialResultSets encodes two rows, one containing the field value "Hello", and a second containing the field value "World" = "W" + "orl" + "d".

chunkedValue

boolean

If true, then the final value in values is chunked, and must be combined with more values from subsequent PartialResultSets to obtain a complete field value.

resumeToken

string (bytes format)

Streaming calls might be interrupted for a variety of reasons, such as TCP connection loss. If this occurs, the stream of results can be resumed by re-sending the original request and including resumeToken. Note that executing any other transaction in the same session invalidates the token.

A base64-encoded string.

stats

object(ResultSetStats)

Query plan and execution statistics for the statement that produced this streaming result set. These can be requested by setting ExecuteSqlRequest.query_mode and are sent only once with the last response in the stream. This field will also be present in the last response for DML statements.

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