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teaching:projh402 [2020/10/03 18:18] ezimanyi [Projects in Mobility Databases] |
teaching:projh402 [2020/10/03 18:20] ezimanyi [VODKA Indexes for MobilityDB] |
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| MobilityDB provides [[https://habr.com/en/company/postgrespro/blog/444742/|GiST]] and [[https://habr.com/ru/company/postgrespro/blog/446624/|SP-GiST]] indexes for temporal types. These indexes are based on bounding boxes, that is, the nodes of the index tree store a bounding box that keeps the mininum and maximum values of each of the dimensions where X, Y, Z (if available) are for the spatial dimension and T for the temporal dimension. The reason for this is that a temporal type (for example, a moving point representing the movement of a vehicle) can have thousands of timestamped points and keeping all these points for each vehicle indexed in a table is very inefficient. By keeping the bounding box only it is possible to quickly filter the rows in a table and then a more detailed analysis can be made for those rows selected by the index. | MobilityDB provides [[https://habr.com/en/company/postgrespro/blog/444742/|GiST]] and [[https://habr.com/ru/company/postgrespro/blog/446624/|SP-GiST]] indexes for temporal types. These indexes are based on bounding boxes, that is, the nodes of the index tree store a bounding box that keeps the mininum and maximum values of each of the dimensions where X, Y, Z (if available) are for the spatial dimension and T for the temporal dimension. The reason for this is that a temporal type (for example, a moving point representing the movement of a vehicle) can have thousands of timestamped points and keeping all these points for each vehicle indexed in a table is very inefficient. By keeping the bounding box only it is possible to quickly filter the rows in a table and then a more detailed analysis can be made for those rows selected by the index. | ||
| - | However, the drawback of keeping a single bounding box for the whole trajectory makes that the index is not very selective as shown in the following figure (extracted from a presentation by Oleg Bartunov from ProstgresPro) | + | However, the drawback of keeping a single bounding box for the whole trajectory makes that the index is not very selective as shown in the following figure (extracted from a presentation by Oleg Bartunov from PostgresPro) |
| {{:teaching:gist.png?400|}} | {{:teaching:gist.png?400|}} | ||