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hstore - Implementation and performance issues around its operators

From: Stefan Keller <sfkeller(at)gmail(dot)com>
To: pgsql-hackers(at)postgresql(dot)org
Subject: hstore - Implementation and performance issues around its operators
Date: 2011-06-21 08:04:12
Message-ID: BANLkTimjZBc9pPzyjcmOarUKcBpf7cJBBA@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Hi,

We did a benchmark comparing a Key-Value-Pairs stored as EAV db schema
versus hstore. The results are promising in favor of hstore but there are some
question which remain.

1. Obviously the '@>' has to be used in order to let use the GiST index.
Why is the '->' operator not supported by GiST ('->' is actually
mentioned in all examples of the doc.)?

2. Currently the hstore elements are stored in order as they are
coming from the insert statement / constructor.
Why are the elements not ordered i.e. why is the hstore not cached in
all hstore functions (like hstore_fetchval etc.)?

3. In the source code 'hstore_io.c' one finds the following enigmatic
note: "... very large hstore values can't be output. this could be
fixed, but many other data types probably have the same issue."
What is the max. length of a hstore (i.e. the max. length of the sum
of all elements in text representation)?

4. Last, I don't fully understand the following note in the hstore
doc. (http://www.postgresql.org/docs/current/interactive/hstore.html
):
> Notice that the old names are reversed from the convention
> formerly followed by the core geometric data types!

Why names? Why not rather 'operators' or 'functions'?
What does this "reversed from the convention" mean concretely?

Yours, Stefan

P.S. I already tried to ask these questions to postgres-performance
and to the hstore authors without success...

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