Hi all,
a month ago this PR that fixes an issue with filter parameters handling in GWC file blob storage:
https://github.com/GeoWebCache/geowebcache/pull/1230
Some context:
- Filter parameters in GWC allow the creation of parallel caches for different parameter values (e.g., time, elevation, viewparam, env, anything hanging an effect on the tile contents)
- Given the parameter contents might be long, complex, and not file system friendly, all blob storages turn them into a summary string, a SHA1, that identifies them (not entirely collision free, but the chance is really low)
- The mapping between the sha1 and the actual set of parameter values is stored too. And here is where the difference is, the cloud storages store it in the same “folder” where the tiles are put, the file system in a single, centralized property file for the layer
The latter is handy, but at the same time, it creates a point of contention among many threads/processes, and the file can grow very large (think of long time series), exacerbating the problem to the point that even just adding a new entry is slow. Add to that a NFS mount, and you have all the elements for a horror movie.
The PR simply aligns the file system blobstore practice with the cloud storage case, where the file has only one entry, is immutable past creation, and if two processes manage to step on each other toas, they would still produce the same file content.
And oh, the code is setup so that there is transparent migration of the entries from the old to the new storage, so nothing is lost.
Soo… objections to backport to stable/maintenance?
···
Regards,
Andrea Aime
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Ing. Andrea Aime
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