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I have a table with an xml column, created an index as follows:

CREATE INDEX xml_index
  ON test
  USING btree
  (((xpath('//*/ChangedBy/text()'::text, external_attributes))[1]::text));

And here is my select statement:

Select uuid from t 
  where  (xpath('//*/ChangedBy/text()', external_attributes))[1]::text = 'User';

I then insert 100rows into this table, then do a select with the above statement.
Explain shows that the query is using the xml_index.

Now I insert 5000 more rows and Explain shows that the query does not use the xml_index anymore.
However, if I drop the index and re create it, then Explain tells me that it's using the index again.

Any ideas what is going on here ?

Thanks
Chris


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