Alternatives to SQL ...
Hi,
I'm wondering about alternative accesses to a PostgreSQL data base
by means other than SQL. I know one can map many things to SQL, but
let me think outside the box for just a moment:
- Sending a parse tree in XML for processing by the optimizer.
This circumvents the SQL language and avoids the kinds of
syntactic ideosyncrasies of SQL (e.g., where you put commas.)
This is fairly trivial, but of course the question is, would
it be worth it?
- Sending an execution plan in XML directly to the executor.
This now circumvents the SQL parser and optimizer. I know this
in in a way against the relational doxology and I don't take that
light-heartedly. However, isn't it true that most optimizers
cannot deal very well with more than 6 joins? I may be wrong,
but I find myself spending quite a bit of time fighting with the
Oracle or PostgreSQL optimizer to convince it to choose the plan
that I want. There is so much magic to it with hints and the
way you write SQL (where in relational theory the expressions are
equivalent, they make huge difference in what plan is being
generated.) So, it appears to me almost easier to just send a
plan directly and have the system execute that plan.
- These direct interfaces could be a nice way to experiment with
new strategies without having to implement it on all three
layers (SQL language, optimizer, and executor.)
You noticed I sneaked in XML as the interface, and that would be
neat because with XSLT it's so easy to manipulate. But I'm also
thinking about a Prolog binding or constraint logic programming
binding, that might be better optimizeable if it goes through a
more direct path than SQL.
Am I crazy?
-Gunther
--
Gunther Schadow, M.D., Ph.D. gschadow@regenstrief.org
Medical Information Scientist Regenstrief Institute for Health Care
Adjunct Assistant Professor Indiana University School of Medicine
tel:1(317)630-7960 http://aurora.regenstrief.org
The SQL interface is bullet-proof because it validates tables, computes
offsets, and stuff like that. Passing something else into the database
and bypassing the SQL stage would require rewriting all the C logic for
SQL to match your new language --- a lot of work for little gain.
---------------------------------------------------------------------------
Gunther Schadow wrote:
Hi,
I'm wondering about alternative accesses to a PostgreSQL data base
by means other than SQL. I know one can map many things to SQL, but
let me think outside the box for just a moment:- Sending a parse tree in XML for processing by the optimizer.
This circumvents the SQL language and avoids the kinds of
syntactic ideosyncrasies of SQL (e.g., where you put commas.)
This is fairly trivial, but of course the question is, would
it be worth it?- Sending an execution plan in XML directly to the executor.
This now circumvents the SQL parser and optimizer. I know this
in in a way against the relational doxology and I don't take that
light-heartedly. However, isn't it true that most optimizers
cannot deal very well with more than 6 joins? I may be wrong,
but I find myself spending quite a bit of time fighting with the
Oracle or PostgreSQL optimizer to convince it to choose the plan
that I want. There is so much magic to it with hints and the
way you write SQL (where in relational theory the expressions are
equivalent, they make huge difference in what plan is being
generated.) So, it appears to me almost easier to just send a
plan directly and have the system execute that plan.- These direct interfaces could be a nice way to experiment with
new strategies without having to implement it on all three
layers (SQL language, optimizer, and executor.)You noticed I sneaked in XML as the interface, and that would be
neat because with XSLT it's so easy to manipulate. But I'm also
thinking about a Prolog binding or constraint logic programming
binding, that might be better optimizeable if it goes through a
more direct path than SQL.Am I crazy?
-Gunther--
Gunther Schadow, M.D., Ph.D. gschadow@regenstrief.org
Medical Information Scientist Regenstrief Institute for Health Care
Adjunct Assistant Professor Indiana University School of Medicine
tel:1(317)630-7960 http://aurora.regenstrief.org---------------------------(end of broadcast)---------------------------
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--
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pgman@candle.pha.pa.us | (610) 853-3000
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On Fri, May 24, 2002 at 12:43:36PM -0500, Gunther Schadow wrote:
- Sending a parse tree in XML for processing by the optimizer.
This circumvents the SQL language and avoids the kinds of
syntactic ideosyncrasies of SQL (e.g., where you put commas.)
This is fairly trivial, but of course the question is, would
it be worth it?
I don't know if you can design something in XML that is expressive and
simple enough to compete with SQL. SQL is a simple language, why replace it
with something unless it is demonstrably better.
- Sending an execution plan in XML directly to the executor.
This now circumvents the SQL parser and optimizer. I know this
in in a way against the relational doxology and I don't take that
light-heartedly. However, isn't it true that most optimizers
cannot deal very well with more than 6 joins? I may be wrong,
but I find myself spending quite a bit of time fighting with the
Oracle or PostgreSQL optimizer to convince it to choose the plan
that I want. There is so much magic to it with hints and the
way you write SQL (where in relational theory the expressions are
equivalent, they make huge difference in what plan is being
generated.) So, it appears to me almost easier to just send a
plan directly and have the system execute that plan.
The detail contained in plans is quite substantial (as you can see using
EXPLAIN VERBOSE). I doubt you can rely on programmers getting all the
details right. As for the join problem, some people get good results tweaking
the genetic query optimiser using documented interfaces. And if you don't
like the way the tables are joined, the INNER/OUTER/LEFT/RIGHT JOIN syntax
in SQL allows you to force the order.
--
Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/
Show quoted text
There are 10 kinds of people in the world, those that can do binary
arithmetic and those that can't.
The world rejoiced as kleptog@svana.org (Martijn van Oosterhout) wrote:
On Fri, May 24, 2002 at 12:43:36PM -0500, Gunther Schadow wrote:
- Sending a parse tree in XML for processing by the optimizer.
This circumvents the SQL language and avoids the kinds of
syntactic ideosyncrasies of SQL (e.g., where you put commas.)
This is fairly trivial, but of course the question is, would it
be worth it?
X-Mailer: mh-e 6.1; nmh 1.0.4+dev; Emacs 21.4
I don't know if you can design something in XML that is expressive
and simple enough to compete with SQL. SQL is a simple language, why
replace it with something unless it is demonstrably better.
SQL is good at providing "linear" queries; queries that indicate some
"linear" relationship between elements.
It is not so good at representing hierarchical relationships, which is
what XML is about.
The SQL:
SELECT FIELDS FROM TABLE
provides you with a linear list.
SQL isn't _nearly_ as nice at representing things that are naturally
expressed as trees. It's pretty easy to have a DB schema where you
essentially have to submit an SQL query for every level of the tree.
And I am not ignoring JOIN here; that adds _some_ ability to join
together levels of trees, but not an unlimited ability.
The XML model fundamentally involves a hierarchy, and the 'query
method' involves passing in a function that reshapes that hierarchy.
I think there would be considerable value to that.
It certainly needs to be thought about before it is implemented, but
it's worth thinking about, to be sure.
--
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http://www.ntlug.org/~cbbrowne/multiplexor.html
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