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fix: empty vector layer reload() will never invalidate cache #60154

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fix: empty vector layer reload() will never invalidate cache #60154

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13 changes: 5 additions & 8 deletions src/core/vector/qgsvectorlayercache.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -388,14 +388,11 @@ void QgsVectorLayerCache::layerDeleted()

void QgsVectorLayerCache::invalidate()
{
if ( ! mCache.isEmpty() )
{
mCache.clear();
mCacheOrderedKeys.clear();
mCacheUnorderedKeys.clear();
mFullCache = false;
emit invalidated();
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We can keep the if condition and just get out the signal firing

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To be honest I cant' remember exactly but I suspect that part of the speed optimization of my original PR was to not fire the signal when the cache was not changed (because it was already empty) .

The fact here is that there are possibly many side effects when firing a signal and some of these can slow down the application significantly.

I would recommend to explore if are there other ways to fix the issue.

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However, the condition only blocks the signal when it is empty, and the signal is still emitted when it is not empty. Is it feasible to add if(mFullCache)?

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@elpaso That would require then to be able to distinguish between an empty cache because of an empty layer, or an empty cache because cache has not been yet populated

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@elpaso That would require then to be able to distinguish between an empty cache because of an empty layer, or an empty cache because cache has not been yet populated

Can we do that? Maybe a flag that is flipped the first time the cache is "populated" (even if empty)?

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or a boolean isLayerEmpty updated when we populate the cache

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@hxbb00 hxbb00 Jan 23, 2025 •
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Can we use mFullCache as a flag? What is the purpose of mFullCache?

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mFullCache stands for "all the layer is in the cache".

Maybe we could replace it with an enum on cache state : EMPTY_LAYER, NOT_INITIALIZED, PARTIAL, FULL

}
mCache.clear();
mCacheOrderedKeys.clear();
mCacheUnorderedKeys.clear();
mFullCache = false;
emit invalidated();
}

bool QgsVectorLayerCache::canUseCacheForRequest( const QgsFeatureRequest &featureRequest, QgsFeatureIterator &it )
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