>On one of my views I need an index but the index keeps vanishing after I have created it.
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>It is a small view. I create the view then create the index with
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>INDEX on seq TAG seq
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>This works with no error messages but no index results afterwards.
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>SET ORDER TO TAG SEQ produces no error message.
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>the ORDER() command returns an empty string
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>Using SET to check the data environment does indeed show there is no index on the view.
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>Is a disk presence required before I can create an index? because I notice that the view only appears in memory and not on disk. This might be my problem.
>
>If so how do I force a disk presence since it does not appear in the view designer.

You have to set the buffering mode of the view to optimistic buffering with:

CURSORSETPROP("BUFFERING", "view_name", 5)

Then you can create your index. Also, the index only lasts until the view is closed. Next time, you have to recreate it.