Обсуждение: SQLJ
All,I've just read in DBMS magazine that Oracle, Informix, etc... are replacing there proprietary Procedural Language's (PL/SQL) with JVMs (JAVA virtual machine). Apparently according to the database vendors, this will obviate the need for middle ware products and to make CORBA much more intuitive. My personal opinion is this is yet another mechanism to slow down the database engine. I don't mind using JAVA in the database engine as a procedural language, but I think there is still great merit in breaking this out as a separate process (Application Server). D.
Dan Gowin wrote: > > I've just read in DBMS magazine that Oracle, Informix, etc... > are replacing there proprietary Procedural Language's (PL/SQL) with > JVMs (JAVA virtual machine). Apparently according to the database > vendors, this will obviate the need for middle ware products and to > make CORBA much more intuitive. This was a problem that I also wanted to talk about. > My personal opinion is this is yet another mechanism to slow down > the database engine. I don't mind using JAVA in the database engine > as a procedural language, but I think there is still great merit in > breaking > this out as a separate process (Application Server). I don't think that it would be slower than PlTcl for example. Talking about speed: I made some tests with some procedures written in PlPgsql and PlTcl! I understood also that PlPgsql is compiling the procedure body into a sort of bytecodes and the execution is somewhat faster. In PlTcl, I feel (I didn't poke the sources) that a PlTcl procedure body is interpreted each time at execution time. For this reason, it doesn't beneffit from Tcl 8.x compiler, making it slowly than PlPgsql. Am I right ? The first question is : Is Tcl 8.x able to precompile a script and return the bytecodes that should be kept into the database and execute them later? >From this point of view, I think that compiling a Java language procedure and storing the resulting .class might be at execution time as faster as PlPgsql. And , I think, perfectly possible. Right now, I am working at a big project using : 1. Tcl/Tk as thin client 2. Messaging server written in Java as a middle-tier with JDBC 3. PostgreSQL RDBMS It would be perfect from me if PostgreSQL will allow procedures written in Java language. -- Constantin Teodorescu FLEX Consulting Braila, ROMANIA
Constantin Teodorescu wrote:
>
> Dan Gowin wrote:
> [...]
>
> > My personal opinion is this is yet another mechanism to slow down
> > the database engine. I don't mind using JAVA in the database engine
> > as a procedural language, but I think there is still great merit in
> > breaking
> > this out as a separate process (Application Server).
>
> I don't think that it would be slower than PlTcl for example.
>
> Talking about speed:
>
> I made some tests with some procedures written in PlPgsql and PlTcl!
> I understood also that PlPgsql is compiling the procedure body into a
> sort of bytecodes and the execution is somewhat faster.
> In PlTcl, I feel (I didn't poke the sources) that a PlTcl procedure body
> is interpreted each time at execution time. For this reason, it doesn't
> beneffit from Tcl 8.x compiler, making it slowly than PlPgsql. Am I
> right ?
>
> The first question is : Is Tcl 8.x able to precompile a script and
> return the bytecodes that should be kept into the database and execute
> them later?
Speaking about the versions of PL/pgSQL and PL/Tcl shipped
with Postgres v6.4 (and bugfix releases).
PL/pgSQL does precompile the source of the function body the
first time, a function is called in a backend. For most of
the statements, even if they are a simple assignment like
"var := 0;", a prepared SPI statement get's created. This
makes PL/pgSQL damned slow and I plan to optimize that by
handling simple expressions that have only one targetlist
entry directly instead of using the SPI manager.
PL/Tcl uses the precompiler of Tcl8.0. Inside the PL handler
module, a safe Tcl interpreter is created at the first of all
calls to one function written in PL/Tcl. All functions called
are somewhat "sourced" into the safe interpreter. Thus, on
multiple invocations of one and the same function, the
Interpreter does reuse the precompiled bytecode it is holding
inside for the procedures. But the programmer must arrange
for usage of prepared and saved SPI execution plans for data
access. The Tcl command "spi_exec", available in PL/Tcl,
really calls SPI_exec - resulting in a parse-rewrite-
optimize-execute sequence for the statement every time.
Using spi_prepare (only on first call of the PL/Tcl function)
and spi_execp instead will gain much performance increase!
Another area that should be optimized sometimes in PL/Tcl is
using the object interface which came with Tcl8.0. Up to now,
the PL/Tcl handler uses the string level C-API only.
I don't think it would be good to remember the generated
bytecode of Tcl itself. This would mean to muck around with
internals of Tcl objects. A clear violation of the OOP
paradigm.
Both languages have performance problems in scenarios like a
WEB environment. By default, any WEB access creates a new
Postgres backend, that has to compile the functions used.
>
> >From this point of view, I think that compiling a Java language
> procedure and storing the resulting .class might be at execution time as
> faster as PlPgsql. And , I think, perfectly possible.
Should (and could) use the same interfacing mechanism as is.
It is just another loadable procedural language handler. And
the design changes we did in the fmgr for v6.3.2 where to
enable these language handlers.
>
> Right now, I am working at a big project using :
> 1. Tcl/Tk as thin client
> 2. Messaging server written in Java as a middle-tier with JDBC
> 3. PostgreSQL RDBMS
>
> It would be perfect from me if PostgreSQL will allow procedures written
> in Java language.
PL/Tcl and PL/pgSQL are the only two languages available,
because noone else than me did anything in that corner up to
now. You're welcome :-).
Jan
--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#======================================== jwieck@debis.com (Jan Wieck) #
Jan Wieck wrote: > > PL/Tcl and PL/pgSQL are the only two languages available, > because noone else than me did anything in that corner up to > now. You're welcome :-). :-) Yeap! Easy to say! Hard to do! I'm not a "core" programmer. I am rather new to Java (only 2 weeks), and I don't know anything about inside PostgreSQL structures. We would need someone with much more expertise in "C", "C++", Java and PostgreSQL than me. -- Constantin Teodorescu FLEX Consulting Braila, ROMANIA
>Jan Wieck wrote: >> >> PL/Tcl and PL/pgSQL are the only two languages available, >> because noone else than me did anything in that corner up to >> now. You're welcome :-). > >:-) > >Yeap! Easy to say! Hard to do! > >I'm not a "core" programmer. I am rather new to Java (only 2 weeks), and >I don't know anything about inside PostgreSQL structures. >We would need someone with much more expertise in "C", "C++", Java and >PostgreSQL than me. I've been interested in this topic too. My idea is having JVM as a separate process from the backend. Maybe JServ(Apache's servlet extension package) is a good starting point. Also it would be nice if the backend could use some functionalities of Java, such as encoding conversions. I am by no means a Java guru, thus this would be a great challenge for me:-) -- Tatsuo Ishii
On Wed, 6 Jan 1999, Tatsuo Ishii wrote: > >Jan Wieck wrote: > >> > >> PL/Tcl and PL/pgSQL are the only two languages available, > >> because noone else than me did anything in that corner up to > >> now. You're welcome :-). > > > >:-) > > > >Yeap! Easy to say! Hard to do! > > > >I'm not a "core" programmer. I am rather new to Java (only 2 weeks), and > >I don't know anything about inside PostgreSQL structures. > >We would need someone with much more expertise in "C", "C++", Java and > >PostgreSQL than me. > > I've been interested in this topic too. My idea is having JVM as a > separate process from the backend. Maybe JServ(Apache's servlet > extension package) is a good starting point. Also it would be nice if > the backend could use some functionalities of Java, such as encoding > conversions. > > I am by no means a Java guru, thus this would be a great challenge for > me:-) I havent touched the native side of Java (have stuck with just pure java so far, and will probably stay that way), but from what I understand on how JNI works: 1. If say PL/Java was implemented _AND_ enabled, then when the postmaster is first started, you can start a JVM as a separate process at that time. While waiting for connections, this JVM would be sitting dormant. 2. When a connection is made to the backend, a Thread (Java not native) is started in the JVM, which creates any objects needed by the PL/Java code. (For performance sake, I'd think this would be done by using a parameter set in the database - that way db's without the need of PL/Java support wouldn't be affected. 3. When a call to a PL/Java procedure is made, then a fresh Thread is made in the JVM, and calls the method to handle the procedure. Obviously this scheme would need the PL/Java functions pre-compiled using the JDK, and the class files (or better still as a single jar file) being introduced to the database. I'd thought that running EcmaScript (what is commonly known as JavaScript) would be too slow. >From my tests using the latest JVM, at least under Windows, it's performance has improved tremendously. It's still slow in starting up, but once running it's pretty good. Also, when running without a GUI, it's better still. Another plus would be CORBA. If, using JNI we had a way of getting at SPI functions, then you could create objects in Java that fed directly into the backend. It would be limited (as only a small part of CORBA 2.0 is in JDK 1.2), but it would be a start. -- Peter T Mount peter@retep.org.uk Main Homepage: http://www.retep.org.uk PostgreSQL JDBC Faq: http://www.retep.org.uk/postgresJava PDF Generator: http://www.retep.org.uk/pdf