Migrating Queries from Previous to Current NDT Unified Views
In July 2020, M-Lab began publishing new “Unified Views” for the NDT dataset in BigQuery. These views function just like tables, but provide only NDT tests that meet our team’s current, best understanding of test completeness and research quality. Combined with our related work to standardize the columns provided in our BigQuery datasets, M-Lab can better enable Long Term Support of stable schemas.
In the long term, this will reduce the number of breaking changes to your queries from schema or field name changes. However, in the short term, this document will aide users in migrating queries to the latest NDT Unified Views.
NDT Protocols Reference
The NDT dataset now contains data from three different NDT protocol types: web100, ndt5, & ndt7. Your past queries may contain field names that were only present in the test results of one of these protocols. More information about the history of the NDT test and protocols hosted by M-Lab can be found on our blog. Our standard columns approach and NDT unified views remove this issue.
NDT Views Reference
We now publish three series of Datasets in BigQuery containing Views for NDT data. These datasets and views mirror the processing stages of our ETL pipeline:
| ||Unified Views in the |
| ||Extended Views in the |
| ||Raw Views in the |
In past documentation and blog posts, Unified Views may also be referred to as “Helpful views”.
This document will focus on migrating queries to use NDT Unified Views
NDT Unified Views Schema Crosswalk
Most of our users are interested in NDT tests that meet our team’s current, best understanding of test completeness and research quality. The NDT Unified Views provide this, and also present a standard set of columns of interest to most people. The current NDT unified views are:
Your queries may be based on several possible tables or views that we published previously. Here we will focus on general strategies for updating your queries. If you find that your queries contain fields not mentioned here, please consult the schemas for each NDT protocol (see links above), or email email@example.com
Updating Table Names in Queries
First, you’ll need to update the tables/views in your queries. Below we list of previously published tables and views, and which tables/views you should use instead. If two tables are listed in the right column, this indicates that the original table included both upload and download tests.
|Previously Published Tables/Views||Recommended Replacement|
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Updating Desired Metrics in Queries
One goal of the NDT Unified Views is to present the most commonly needed test metrics and metadata in the first part of the views’ schemas. For quick reference, those fields are listed below.
|id||The Universally Unique Identifier assigned to this test|
|date||The date this test was run in UTC|
|a. UUID||The Universally Unique Identifier assigned to this test|
|a. TestTime||The date and time this test was conducted in UTC|
|a. CongestionControl||The TCP congestion control algorithm used during this measurement. One of: reno, cubic,bbr|
|a. MeanThroughputMbps||The download or upload throughput measured in Megabits per second|
|a. MinRTT||The Minimum Round Trip Time in milliseconds|
|a. LossRate||The packet loss rate in milliseconds|
|node. _Instruments||Indicates the server-side instrumentation that provided measurements for this test. One of: web100, tcpinfo, ndt7|
Previously some metrics like upload or download throughput had to be calculated from component fields. For example in web100 NDT data, download throughput was calculated in a query using this formula:
(8 * web100_log_entry.snap.HCThruOctetsAcked/ (web100_log_entry.snap.SndLimTimeRwin + web100_log_entry.snap.SndLimTimeCwnd + web100_log_entry.snap.SndLimTimeSnd)
The new NDT Unified Views provide upload and download throughput as a single field:
a.MeanThroughputMbps. It is labelled “Mean” because it is the average of each TCP snapshot that occurs during every NDT test. If you need upload throughput, select
measurement-lab.ndt.unified_uploads, or download throughput from
If your research requires access to additional metrics not present in the NDT Unified Views, please review Obtaining Additional Metrics from Intermediate or Raw Tables & Views,
Name Changes to Annotated Fields
Many fields in our NDT tables and views are annotations based on the IP address for each test. In most cases, these fields’ names have not changed, or are similar, but their full path in the schema structure has been simplified. Below we provide a brief example of some of these fields from previous schemas, and their equivalents in the NDT Unified Views:
Obtaining Additional Metrics from Intermediate or Raw Tables and Views
Another goal of the NDT Unified Views is to simplify the schema to support the majority of users. For researchers who need access to additional metrics from the measurement, or TCP internal statistics that were gathered during the measurement, a join or match is necessary to access the relevant fields from the raw measurement tables or other related tables and views.
If you don’t see a field that you need in the unified views, the next step is to see if the field is available in the Faithful view for the test protocol. The entire list of fields collected by TCPINFO for an ndt7 test are available in:
measurement-lab.ndt.ndt7 in the
raw record. For example, if we wanted to include the TCP Window Scale measured during an upload test, we could select the field:
These can be pulled into your query by matching on the test UUID, for example:
WHERE ndt.unified_downloads.a.UUID = ndt.ndt7.id
The UUID field is a unique ID for each TCP connection to any of our servers, and is very useful for matching and joining generally.
Non-equivalent TCP Metrics Across NDT Protocol Types
One result of our change to the TCP Kernel Instrumention discussed in our blog post, The Evolution of NDT, is that some fields available in the NDT web100 datatype are no longer provided or don’t have equivalents from TCP_INFO, which replaced web100 in Nov. 2019.
The NDT Unified Views present the metrics and fields common across all NDT datatypes (web100, ndft5, ndt7). However, some additional metrics may be available in one or two datatypes, but not all. For example, consider the query below that returned data from the web100 NDT datatype:
SELECT web100_log_entry.snap.MaxRTT AS maxRTT, web100_log_entry.snap.MinRTT AS minRTT FROM `measurement-lab.ndt.recommended` WHERE connection_spec.client_geolocation.city = 'Salt Lake City' AND connection_spec.client_geolocation.region = 'UT' AND web100_log_entry.snap.MaxRTT > 0 AND web100_log_entry.snap.MinRTT > 0
In the NDT Unified Views,
MaxRTT is not present. However, for ndt5 and web100 datatypes, this field can still be accessed and compared.
MaxRTT is available in:
If you find that there are commonly used fields that should be included in the NDT Unified Views, please email us at firstname.lastname@example.org.