Is "Clearing Cache" useful?When and why?

[PersistentDigger]

I often hear (in Local Chat) other avatars saying they are going to log off, clear cache and log back in again.

Now, if I TP to a different sim/parcel, it can often take a little while for the textures and meshes (especially avatar bodies) to either change from grey or become visible. I am thinking that this must be my cache getting re-populated. Myself, I just wait.

Can anyone give me an Idiot's guide to this matter? OR pass on a Link to an imformative page.

[EDIT :- Reply to the Replies]

All three answers were clear and helpful - and it was worth distinguising between the types of Cache.

I think I can safely continue as before and not bother with clearing Textures,etc

And Madelaine, my spade rarely disturbs the sub-soil ...

[Theresa Tennyson]

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PersistentDigger wrote:

I often hear (in Local Chat) other avatars saying they are going to log off, clear cache and log back in again.

Now, if I TP to a different sim/parcel, it can often take a little while for the textures and meshes (especially avatar bodies) to either change from grey or become visible. I am thinking that this must be my cache getting re-populated. Myself, I just wait.

Can anyone give me an Idiot's guide to this matter? OR pass on a Link to an imformative page.

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Clearing cache was a recommended cure-all a few years ago when the system for sending information back and forth was less reliable. It's seldom necessary now and actually slow things down most of the time. Some people still do it out of habit but it is only useful in limited circumstances.

There are actually two separate caches - one for textures and one for the local index of your inventory. Clearing the texture cache is only useful if some of the textures in it are somehow corrupt or incorrect - i.e. radically different from how they should look. This happens sometimes but it's quite seldom and you'll see when it happens.

Clearing your inventory cache can be useful if some of your items appear to be missing from your inventory, but clearing it out of habit will just make it more likely that the complete index won't arrive in the first place.

[Rolig Loon]

Your texture cache is there to make it so that your graphics card does not need to download each individual texture that you see in world, every time  that you see it.  Storing textures locally on your hard drive reduces rendering lag dramatically.  The larger you cache is, the less extra work your system has to do.  Clearing your cache means starting all over again, forcing the viewer to start the tedious business of downloading and saving every single texture that you see in world.  Until it has done that, you will have a lot of gray, untextured SL to look at.

Your computer also caches your inventory and any sounds that you hear in world, again as a way to reduce the amount of time that your viewer has to spend downloading the same things over and over again.  There are occasionally some good reasons for clearing cache and forcing a new download.  If your cached inventory is damaged, for example, you can normally recover lost items by forcing the SL servers to download your inventory again, this reloading your inventory cache. Just as with the texture cache, though, that means you will have a period of low performance until the download is complete.

The bottom line is that you should rarely need to clear your cache.  If you do, expect to have reduced performance for a while.

Take a very good look at

http://wiki.phoenixviewer.com/cache

and

http://wiki.phoenixviewer.com/fs_cache_clear

[Madelaine McMasters]

I'll expand further on Theresa's mention of improved data transfer, and fewer cache errors. At the dawn of SL, many of the data transfers between SL servers and your viewer were done via UDP. This protocol is simple, fast, and has no error detection/correction. This allowed SL to work, but resulted in occasional data corruption. For this reason, we found ourselves needing to flush bad textures from cache now and then.

As internet speeds grew, the cost of providing reliable data transport declined to the point where SL ran fine using more robust protocols. Hence the introduction of HTTP textures a few years ago. The HTTP protocol, which is used to transport web pages across the net, has inherent error detection and correction. Once the SL viewer switched to HTTP for textures, the need to flush the texture cache pratically vanished.

There may still be rare cases where a glitch in the viewer or an SL server causes the corruption of a texture, so the cache clearing mechanism remains. The inventory cache, for reasons unknown to me, still appears to be vulnerable to corruption, and so we often get people asking for help recoving missing inventory. The solution there is still to clear the inventory cache, then go to a quiet region and patiently wait for the inventory cache to rebuid.

And as mentioned by Rolig, clearing any cache will cause a temporary spike in downloads to the viewer (and resulting lag) as the cache contents are reloaded from the SL servers. That's why you don't want to do it unless it's necessary.

We can hope that Sansar is even more robust, and the need for cache clearing goes away forever.

And finally, a comment about your name. Persistence is wonderful, but if you ever find yourself stuck in a hole... stop digging!

;-).