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Storage providers do not use diffs to store changes
At least in the files system storage provider, each change is stored as a complete NEW file.
When comparisons are made, they are made one file against the other.
It is believed that this model is used for all (file-system, db, etc) storage providers.
Over time, with changes, this leads to a large amount of storage bloat.
See the PmWiki model (at least) for storage that stores only the diff of changes (and can still restore back to any version).
Adjusting the storage providers to store as diffs might be a breaking change for some extensions (or maybe not, I don't know).
If at all possible, we should probably make it a config option -- but the default option to use the diffs, and configurable to use non-diffs.