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Also, ADS data requests have limits in terms of number of fields and volume size, which are different for each dataset (see the "Datasets" Table 2 below). These values are dependent on each dataset's structure and where the dataset is actually stored. Again, these restrictions are introduced to help the system maintain good performance and minimise the queuing time for all users.
For example, when a user ADS web request exceeds the number of fields limit, an information message appears at the bottom of the web interface page (Figure 3). Please note, that these limits are also enforced for requests sent via the CDS API.
Figure 3 Information message when a user ADS web request exceeds the number of fields limit.
Datasets
Table 2 Summary of the number of fields limits, as well as the major features of all ADS datasets (last reviewed on 17 June 16 September 2021)
| Dataset | Number of fields limit | Adaptor (indicates where the data are stored; see "Efficiency Tips" below) | Notes |
| 10000 | MARS Internal/external | Those variables listed as fast-access are readily available from ADS disks. Those variables listed as slow-access and data older than 30 days are stored in ECMWF MARS tape archive. | |
| 100000 | MARS Internal/external | Those variables listed as fast-access are readily available from ADS disks. Those variables listed as slow-access are stored in ECMWF MARS tape archive. | |
| 100000 | MARS Internal | N/A | |
CAMS global inversion-optimised greenhouse gas fluxes and concentrations | 500 | adaptor.url | Stored locally on ADS disks |
| 100000 | MARS external | Data are stored in ECMWF MARS tape archive | |
CAMS global greenhouse gas reanalysis (EGG4) monthly averaged fields | 100000 | MARS external | Data are stored in ECMWF MARS tape archive |
| 10000 | adaptor.cams_solar_rad2.retrieve | This data is calculated on demand by a service jointly provided by DLR, Armines, and Transvalor. The ADS forwards requests to this service and returns the data from it. | |
| 5000 | adaptor.cams_regional_fc.retrieve | There are three classes of speed at which these requests will be processed:
| |
| 1000 | adaptor.url | Check the documentation for data availability | |
| 1000 | adaptor.url2.retrieve | N/A | |
| 1000 | adaptor.url | ||
| 1000 | adaptor.url |
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