Alvaro Herrera wrote:
>> Just out of curiosity: Does Postgress store a duplicate of the data in the
index, even for long strings? I thought indexes only had to store the
string up to the point where there was no ambiguity, for example, if I have
"missing", "mississippi" and "misty", the index only needs "missin",
"missis" and "mist" in the actual index.
What would happen when you inserted a new tuple with just "miss"? You
would need to expand all the other tuples in the index.
That's right. This technique used by some index implementations is a tradeoff between
size and update speed. Most words in most natural languages can be distinguished by the
first few characters. The chances of having to modify more than a few surrounding nodes
when you insert "miss" is small, so some implementations choose this method.
Other implementations choose to store the full string. I was just curious which method
Postgres uses.
Craig
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