When searching for approximate nearest neighbors of a vector with regular query API, you specify a topK so that the vector index returns at most that many results. In regular query API, it is not possible to continue the query where it is left off, as each query runs from start to completion, before returning a response. However, there might be cases where you want to get the next topK many similar vectors after running a regular query. Perhaps, you wanted to fetch the next batch of vectors for the next page of your search functionality. Resumable query helps you to achieve that. It has the same features as the regular query; you can specify a filter, get values, metadata or data of the vectors, or specify a topK value. But, after getting the initial response from the server, it allows you to query for more, starting from where it left off instead of the start.

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Starting a Resumable Query

Each resumable query starts in this phase. Using our SDKs or the REST API, you can initiate a resumable query. The filter or flags to include vector values, metadata, or data will be valid for the entire duration of the resumable query. When you start the query, the server responds with the first batch of the most similar vectors and a handle that uniquely identifies the query so that you can continue the query where you left off. 
from upstash_vector import Index

index = Index(
    url="UPSTASH_VECTOR_REST_URL",
    token="UPSTASH_VECTOR_REST_TOKEN",
)

result, handle = index.resumable_query(
    vector=[0.1, 0.2],
    top_k=2,
    include_metadata=True,
)

# first batch of the results
for r in result:
    print(r)
We support resumable queries with raw vector values as shown above, or with raw text data for indexes created with Upstash hosted embedding models.

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Resuming the Resumable Query

Using the handle returned by the initial call to resumable query, you can get the next batch of the most similar vectors, starting from the last response. You can fetch as many next batch as possible until you iterate over the entire index. 
# next batch of the results
next_result = handle.fetch_next(
    additional_k=3,
)

for r in next_result:
    print(r)

# it is possible to call fetch_next more than once
next_result = handle.fetch_next(
    additional_k=5,
)

for r in next_result:
    print(r)

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Stopping the Resumable Query

Each resumable query requires us to maintain a state in the server. So, there is a limit for the maximum number of active resumable queries at a time. That’s why it is important to stop the resumable query once you are done with it. Resumable queries can be stopped using the handle returned with the initial call. 
handle.stop()
We periodically scan resumable queries to stop the idle ones, so queries that have not touched for some time are stopped automatically. By default, the max idle time of a resumable query is 1 hour. You can configure this behavior by specifying a max idle time in seconds while starting the resumable query. 
result, handle = index.resumable_query(
    vector=[0.1, 0.2],
    top_k=2,
    include_metadata=True,
    max_idle = 7200, # two hours, in seconds
)