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Purpose of ASYNC API

The ASYNC API is a programmatic access for asynchronous responses to large data requests.

For the SDMX APIs, data can be returned either synchronously or asynchronously:

  • Synchronously: the data is returned directly in the response to the request. This is the default operation

  • Asynchronously: the data is not returned directly in the response. Instead a key is returned in the response which allows to access the data through the async API to check for its availability and eventually retrieve it once available.

The decision whether to deliver the data synchronously or asynchronously is related to factors such as the complexity of the query and the volume of the data (number of rows) to be returned.

In case the requested filtered data would be to important to be prepared, a client error code 413 is returned with a suggestion to apply more filtering to the request.

<S:Fault xmlns:S="http://schemas.xmlsoap.org/soap/envelope/">
	<faultcode>413</faultcode>
	<faultstring>EXTRACTION_TOO_BIG: The requested extraction is too big, estimated 420709314 rows, max authorised is 5000000, please change your filters to reduce the extraction size</faultstring>
</S:Fault>

When a data request is initiated, the system first checks if the exact same request was already performed previously and if applicable lookup the data directly from an internal cache and return it as a response.
If the data is not cached, the data needs to be extracted and the system estimates the related "extraction cost" in term of potential number of data cells returned.
To compute this cost, the system resolves the number of positions matched by each dimension filter.

As an example, if a dataset has 3 dimensions with respectively 5, 10 and 20 positions available for each dimension, the dataset cardinality is 5 x 10 x 20 = 1000 cells.
An extraction request asking for:

  • 3 positions for the first dimension
  • 2 positions for the second dimension
  • no filtering for the third dimension
    will potentially match 3 x 2 x 20 = 120 cells which is also the estimated cost of this request.

The decision whether to deliver the data synchronously or asynchronously is related to factors such as the complexity of the query and the volume of the data (number of cells) to be returned:

  • if the data is cached -> the data is returned synchronously
  • if the data has to be extracted, the "cost" of the request is estimated and:

In order to know how many positions are available for the dimensions of a dataset, the API provides an SDMX endpoint which returns the SDMX data constraints artefact for the specified dataset.

Taking Eurostat Comext dataset DS-045409 as example, its data constraints can be retrieved using:
https://ec.europa.eu/eurostat/api/comext/dissemination/sdmx/2.1/contentconstraint/estat/DS-045409

In this dataset, the dimensions have the following number of positions:

  • freq has 2 positions
  • reporter has 33 positions
  • partner has 282 positions
  • product has 40321 positions
  • flow has 2 positions
  • time_period has 468 positions (36 years and 432 months)
  • indicators has 3 positions

The dataset cardinality is then: 2 x 33 x 282 x 40321 x 2 x 468 x 3 = 2 107 276 101 216 cells.

Examples queries

1 - Query in range for asynchronous extraction

Following query would be considered within limits and processed by the system 

http://ec.europa.eu/eurostat/api/comext/dissemination/sdmx/2.1/data/DS-045409/A.DK.US..1.SUPPLEMENTARY_QUANTITY?format=SDMX_2.1_STRUCTURED

This query matches the following positions:

  • freq -> 1 position ("A")
  • reporter 1 position ("DK")
  • partner -> 1 position ("US")
  • product -> 40321 positions (there is no filter on this dimension)
  • flow -> 1 position ("1")
  • time_period -> 36 positions (there is no explicit filter on this dimension but the system will only return yearly data)
  • indicators -> 1 position ("SUPPLEMENTARY_QUANTITY")

Estimated cost: 1 x 1 x 1 x 40321 x 1 x 36 x 1 = 1 451 556 which is above the synchronous limit but below the maximum extraction limit so this request is treated asynchronously.

2 -Query above range for asynchronous extraction

Following query would be considered off limits and not processed by the system 

https://ec.europa.eu/eurostat/api/comext/dissemination/sdmx/2.1/data/DS-045409/A.PT...2.QUANTITY_IN_100KG?format=SDMX_2.1_STRUCTURED1

This query matches the following positions:

  • freq -> 1 position ("A")
  • reporter 1 position ("PT")
  • partner -> 282 positions (there is no filter on this dimension)
  • product -> 40321 positions (there is no filter on this dimension)
  • flow -> 1 position ("2")
  • time_period -> 36 positions (there is no explicit filter on this dimension but the system will only return yearly data as the frequency requested is annual)
  • indicators -> 1 position ("QUANTITY_IN_100KG")

Estimated cost: 1 x 1 x 282 x 40321 x 1 x 36 x 1 = 409 338 792 which is above the maximum extraction limit of 5 000 000 cells and an error is returned.


How to implement asynchronous requests?

The asynchronous delivery process can be summarised as follows:

  1. Step 1. A client issues a request to one of the SDMX data API. The API returns a response indicating asynchronous delivery pattern, with a unique key

  2. Step 2. The client issues to the asynchronous endpoint at regular interval a request with the unique key, to enquire about the readiness of the requested data

  3. Step 3. Once the data is available, the client can request the data for the provided unique key and receive it

Example

Step 1: Initial request

For an initial data request for which asynchronous delivery pattern must be used, the response is similar to following XML:

<env:Envelope xmlns:env="http://schemas.xmlsoap.org/soap/envelope/">
	<env:Header/>
	<env:Body>
		<ns0:syncResponse xmlns:ns0="http://estat.ec.europa.eu/disschain/soap/extraction">
			<processingTime>412</processingTime>
			<queued>
				<id>98de05ea-540a-43d3-903b-7c9e14faf808</id>
				<status>SUBMITTED</status>
			</queued>
		</ns0:syncResponse>
	</env:Body>
</env:Envelope>

The <id> value, 98de05ea-540a-43d3-903b-7c9e14faf808 in this example is the key to use for checking data availability against the asynchronous API.

Step 2: Get the current status of the request

The status of a request that is processed asynchronously can be one of the following values:

Value

Meaning

SUBMITTED

The request is queued for processing

PROCESSING

The request is currently being processed

AVAILABLE

The data is available for download,

EXPIRED

The data is no longer available. This occurs after a few days or when corresponding dataset content was updated. Please restart from Step 1.

UNKNOWN_REQUEST

In case the key provided cannot be matched to a request

ERROR

The request was processed but an unexpected error occurred.

Please retry or contact support with id of your request

The current status of a given request can be obtained via a REST request:

This request may provide different results, depending on the current status of the request:

  • PROCESSING : As long as the request is not processed/finished, the following result will be returned:

    <env:Envelope xmlns:env="http://schemas.xmlsoap.org/soap/envelope/">
	<env:Header/>
	<env:Body>
		<ns0:asyncResponse xmlns:ns0="http://estat.ec.europa.eu/disschain/soap/asynchronous" xmlns:ns1="http://estat.ec.europa.eu/disschain/asynchronous">
			<ns1:status>
				<ns1:key>98de05ea-540a-43d3-903b-7c9e14faf808</ns1:key>
				<ns1:status>PROCESSING</ns1:status>
			</ns1:status>
		</ns0:asyncResponse>
	</env:Body>
</env:Envelope>

  • AVAILABLE: The request is processed/finished. When the query is fully executed, the returned status will be AVAILABLE and the following result will be returned:

    <env:Envelope xmlns:env="http://schemas.xmlsoap.org/soap/envelope/">
	<env:Header/>
	<env:Body>
		<ns0:asyncResponse xmlns:ns0="http://estat.ec.europa.eu/disschain/soap/asynchronous" xmlns:ns1="http://estat.ec.europa.eu/disschain/asynchronous">
			<ns1:status>
				<ns1:key>98de05ea-540a-43d3-903b-7c9e14faf808</ns1:key>
				<ns1:status>AVAILABLE</ns1:status>
			</ns1:status>
		</ns0:asyncResponse>
	</env:Body>
</env:Envelope>

Step 3: Get the data

When the results are AVAILABLE, it is possible to to download the data. Data can be obtained via a REST request:

Errors returned

No data 

In case the query eventually did not contains any statistical value, 

<S:Fault xmlns:S="http://schemas.xmlsoap.org/soap/envelope/">
	<faultcode>100</faultcode>
	<faultstring>NO_RESULTS: The query that has been sent did not return any results.</faultstring>
</S:Fault>


Data not yet ready

As long as the data is not ready as informed by the status service call, the returned XML response will be:

<S:Fault>
	<faultcode>100</faultcode>
    <faultstring>DATA_NOT_YET_AVAILABLE: Requested data is not yet available for download. Check the status of your request.</faultstring>
</S:Fault>
Invalid key

If the key provided is not valid, the returned SOAP result will be:

<S:Fault>
	<faultcode>100</faultcode>
    <faultstring>UNKNOWN_REQUEST: Unknown request.</faultstring>
</S:Fault>
Invalid key
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