Thread: Re: How do BEGIN/COMMIT/ABORT operate in a nested SPI query?

I am attempting to create a new language implementation. The language is Andl (andl.org), so the handler is plandl.
This is a question about executing SPI queries from inside plandl.

The documentation makes it clear that SPI allows nested queries; that in some instances it will be necessary to call
SPI_push()and SPI_pop(), but in others this will be handled automatically. Se
http://www.postgresql.org/docs/9.5/interactive/spi-spi-push.html.

It is an important design feature of plandl to allow nested queries.

My question is: where are the transaction boundaries if the inner/outer query do or do not contain BEGIN/ABORT/COMMIT?
Dothey nest, or does an inner COMMIT finish a transaction started by an outer BEGIN, or is it ignored? 

Regards
David M Bennett FACS

Andl - A New Database Language - andl.org

david@andl.org wrote:
> I am attempting to create a new language implementation. The language is Andl (andl.org), so the
> handler is plandl.
> This is a question about executing SPI queries from inside plandl.
> 
> The documentation makes it clear that SPI allows nested queries; that in some instances it will be
> necessary to call SPI_push() and SPI_pop(), but in others this will be handled automatically. Se
> http://www.postgresql.org/docs/9.5/interactive/spi-spi-push.html.
> 
> It is an important design feature of plandl to allow nested queries.
> 
> My question is: where are the transaction boundaries if the inner/outer query do or do not contain
> BEGIN/ABORT/COMMIT? Do they nest, or does an inner COMMIT finish a transaction started by an outer
> BEGIN, or is it ignored?

You cannot have BEGIN or COMMIT inside a function.

Yours,
Laurenz Albe

> From: Albe Laurenz [mailto:laurenz.albe@wien.gv.at]
>
> > I am attempting to create a new language implementation. The language
> > is Andl (andl.org), so the handler is plandl.
> > This is a question about executing SPI queries from inside plandl.
> >
> > The documentation makes it clear that SPI allows nested queries; that
> > in some instances it will be necessary to call SPI_push() and
> > SPI_pop(), but in others this will be handled automatically. Se
> http://www.postgresql.org/docs/9.5/interactive/spi-spi-push.html.
> >
> > It is an important design feature of plandl to allow nested queries.
> >
> > My question is: where are the transaction boundaries if the
> > inner/outer query do or do not contain BEGIN/ABORT/COMMIT? Do they
> > nest, or does an inner COMMIT finish a transaction started by an outer
> BEGIN, or is it ignored?
>
> You cannot have BEGIN or COMMIT inside a function.

Are you sure you meant it like that? I already have BEGIN/COMMIT inside a function and it works perfectly. If it did
not,then it would be impossible to use BEGIN/COMMIT in any language handler, since every call to a language handler is
acall to a function. 

Did you mean 'inside a nested function'? Or something else?

Regards
David M Bennett FACS

Andl - A New Database Language - andl.org

On 4/18/2016 5:41 PM, david@andl.org wrote:
> Are you sure you meant it like that? I already have BEGIN/COMMIT inside a function and it works perfectly. If it did
not,then it would be impossible to use BEGIN/COMMIT in any language handler, since every call to a language handler is
acall to a function. 

the transaction has already been started before your function is called.

and you can not issue a COMMIT from anywhere but the top level. you CAN
have savepoints, which act something like  nested transactions within a
function.



--
john r pierce, recycling bits in santa cruz

> From: Albe Laurenz [mailto:laurenz.albe@wien.gv.at]
>
> > I am attempting to create a new language implementation. The language
> > is Andl (andl.org), so the handler is plandl.
> > This is a question about executing SPI queries from inside plandl.
> >
> > The documentation makes it clear that SPI allows nested queries; that
> > in some instances it will be necessary to call SPI_push() and
> > SPI_pop(), but in others this will be handled automatically. Se
> http://www.postgresql.org/docs/9.5/interactive/spi-spi-push.html.
> >
> > It is an important design feature of plandl to allow nested queries.
> >
> > My question is: where are the transaction boundaries if the
> > inner/outer query do or do not contain BEGIN/ABORT/COMMIT? Do they
> > nest, or does an inner COMMIT finish a transaction started by an outer
> BEGIN, or is it ignored?
>
> You cannot have BEGIN or COMMIT inside a function.

Are you sure you meant it like that? I already have BEGIN/COMMIT inside a function and it works perfectly. If it did
not,then it would be impossible to use BEGIN/COMMIT in any language handler, since every call to a language handler is
acall to a function. 

Did you mean 'inside a nested function'? Or something else?

Regards
David M Bennett FACS

Andl - A New Database Language - andl.org

David Bennett wrote:
> > From: Albe Laurenz [mailto:laurenz.albe@wien.gv.at]
> >
> > > I am attempting to create a new language implementation. The language
> > > is Andl (andl.org), so the handler is plandl.
> > > This is a question about executing SPI queries from inside plandl.
> > >
> > > The documentation makes it clear that SPI allows nested queries; that
> > > in some instances it will be necessary to call SPI_push() and
> > > SPI_pop(), but in others this will be handled automatically. Se
> > http://www.postgresql.org/docs/9.5/interactive/spi-spi-push.html.
> > >
> > > It is an important design feature of plandl to allow nested queries.
> > >
> > > My question is: where are the transaction boundaries if the
> > > inner/outer query do or do not contain BEGIN/ABORT/COMMIT? Do they
> > > nest, or does an inner COMMIT finish a transaction started by an outer
> > BEGIN, or is it ignored?
> >
> > You cannot have BEGIN or COMMIT inside a function.
> 
> Are you sure you meant it like that? I already have BEGIN/COMMIT inside a function and it works
> perfectly. If it did not, then it would be impossible to use BEGIN/COMMIT in any language handler,
> since every call to a language handler is a call to a function.
> 
> Did you mean 'inside a nested function'? Or something else?

I guess I'm out of my depth when it comes to language handlers...

But I cannot see how you can have BEGIN or COMMIT called from inside one.

Doesn't it look like that:

BEGIN;
SELECT my_andl_function();
COMMIT;

Since there are no autonomous transactions in PostgreSQL, how can you have
BEGIN and COMMIT called from the code that is invoked by "SELECT my_andl_function()"?

Yours,
Laurenz Albe

> From: Albe Laurenz [mailto:laurenz.albe@wien.gv.at]
> > > > I am attempting to create a new language implementation. The
> > > > language is Andl (andl.org), so the handler is plandl.
> > > > This is a question about executing SPI queries from inside plandl.
> > > >
> > > > The documentation makes it clear that SPI allows nested queries;
> > > > that in some instances it will be necessary to call SPI_push() and
> > > > SPI_pop(), but in others this will be handled automatically. Se
> > > http://www.postgresql.org/docs/9.5/interactive/spi-spi-push.html.
> > > >
> > > > It is an important design feature of plandl to allow nested queries.
> > > >
> > > > My question is: where are the transaction boundaries if the
> > > > inner/outer query do or do not contain BEGIN/ABORT/COMMIT? Do they
> > > > nest, or does an inner COMMIT finish a transaction started by an
> > > > outer
> > > BEGIN, or is it ignored?
> > >
> > > You cannot have BEGIN or COMMIT inside a function.
> >
> > Are you sure you meant it like that? I already have BEGIN/COMMIT
> > inside a function and it works perfectly. If it did not, then it would
> > be impossible to use BEGIN/COMMIT in any language handler, since every call
> to a language handler is a call to a function.
> >
> > Did you mean 'inside a nested function'? Or something else?
>
> I guess I'm out of my depth when it comes to language handlers...
>
> But I cannot see how you can have BEGIN or COMMIT called from inside one.
>
> Doesn't it look like that:
>
> BEGIN;
> SELECT my_andl_function();
> COMMIT;
>
> Since there are no autonomous transactions in PostgreSQL, how can you have
> BEGIN and COMMIT called from the code that is invoked by "SELECT
> my_andl_function()"?

I really don't know. But I have code that does this (no explicit BEGIN):

SELECT * FROM COMPILE($$
V6 := {{ abo:=true, abi:=b'DEADBEEF', anu:=123456789.987654321, ate:='abcdef', ati:=t'2015-12-31 23:59:58.9999' },
       { abo:=false, abi:=b'DEADBEEF', anu:=987654321.123456789, ate:='ghijklmno', ati:=t'2016-12-31 23:59:58.9999' }}
V6
$$);

And the generated code (which executes without error):
BEGIN;
DROP TABLE IF EXISTS "V6" ;
CREATE TABLE "V6" ( "abo" BOOLEAN, "abi" BYTEA, "anu" NUMERIC, "ate" TEXT, "ati" TIMESTAMP, UNIQUE ( "abo", "abi",
"anu","ate", "ati" ) ); 
COMMIT;
INSERT INTO "V6" ( "abo", "abi", "anu", "ate", "ati" ) VALUES ( $1, $2, $3, $4, $5 );
SELECT "abo", "abi", "anu", "ate", "ati" FROM "V6";

Maybe the generated BEGIN/COMMIT are ignored? I haven't tried an ABORT yet.

Regards
David M Bennett FACS

Andl - A New Database Language - andl.org

<david@andl.org> writes:
>> From: Albe Laurenz [mailto:laurenz.albe@wien.gv.at]
>> Since there are no autonomous transactions in PostgreSQL, how can you have
>> BEGIN and COMMIT called from the code that is invoked by "SELECT
>> my_andl_function()"?

> I really don't know. But I have code that does this (no explicit BEGIN):

> SELECT * FROM COMPILE($$
> V6 := {{ abo:=true, abi:=b'DEADBEEF', anu:=123456789.987654321, ate:='abcdef', ati:=t'2015-12-31 23:59:58.9999' },
>        { abo:=false, abi:=b'DEADBEEF', anu:=987654321.123456789, ate:='ghijklmno', ati:=t'2016-12-31 23:59:58.9999'
}}
> V6
> $$);

> And the generated code (which executes without error):

> BEGIN;
> DROP TABLE IF EXISTS "V6" ;
> CREATE TABLE "V6" ( "abo" BOOLEAN, "abi" BYTEA, "anu" NUMERIC, "ate" TEXT, "ati" TIMESTAMP, UNIQUE ( "abo", "abi",
"anu","ate", "ati" ) ); 
> COMMIT;
> INSERT INTO "V6" ( "abo", "abi", "anu", "ate", "ati" ) VALUES ( $1, $2, $3, $4, $5 );
> SELECT "abo", "abi", "anu", "ate", "ati" FROM "V6";

Define "executes".  You could shove those lines in via the wire protocol,
sure, but SPI won't take them.

            regards, tom lane

> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>
> > I really don't know. But I have code that does this (no explicit BEGIN):
>
> > SELECT * FROM COMPILE($$
> > V6 := {{ abo:=true, abi:=b'DEADBEEF', anu:=123456789.987654321,
> ate:='abcdef', ati:=t'2015-12-31 23:59:58.9999' },
> >        { abo:=false, abi:=b'DEADBEEF', anu:=987654321.123456789,
> > ate:='ghijklmno', ati:=t'2016-12-31 23:59:58.9999' }}
> > V6
> > $$);
>
> > And the generated code (which executes without error):
>
> > BEGIN;
> > DROP TABLE IF EXISTS "V6" ;
> > CREATE TABLE "V6" ( "abo" BOOLEAN, "abi" BYTEA, "anu" NUMERIC, "ate"
> > TEXT, "ati" TIMESTAMP, UNIQUE ( "abo", "abi", "anu", "ate", "ati" ) );
> > COMMIT; INSERT INTO "V6" ( "abo", "abi", "anu", "ate", "ati" ) VALUES
> > ( $1, $2, $3, $4, $5 ); SELECT "abo", "abi", "anu", "ate", "ati" FROM
> > "V6";
>
> Define "executes".  You could shove those lines in via the wire protocol,
> sure, but SPI won't take them.

Now you really have me puzzled. What I provided is an extract from the log
of generated SQL commands sent to the SPI interface. [Obviously there also
values bound to the parameters which do not show up here.]

The code executes without error and produces exactly the output I expected.

I'll do some more checking to see if I missed something, but so far it just
works.

Regards
David M Bennett FACS

Andl - A New Database Language - andl.org

<david@andl.org> writes:
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>> Define "executes".  You could shove those lines in via the wire protocol,
>> sure, but SPI won't take them.

> Now you really have me puzzled. What I provided is an extract from the log
> of generated SQL commands sent to the SPI interface. [Obviously there also
> values bound to the parameters which do not show up here.]

> The code executes without error and produces exactly the output I expected.

Are you remembering to check the result code from SPI_execute_whatever?

            regards, tom lane

> >> Define "executes".  You could shove those lines in via the wire
> >> protocol, sure, but SPI won't take them.
>
> > Now you really have me puzzled. What I provided is an extract from the
> > log of generated SQL commands sent to the SPI interface. [Obviously
> > there also values bound to the parameters which do not show up here.]
>
> > The code executes without error and produces exactly the output I
expected.
>
> Are you remembering to check the result code from SPI_execute_whatever?

Of course. Every SPI call is checked and any unexpected error is trapped,
resulting eventually in a call to elog(ERROR).

The sequence I provided is a CREATE TABLE followed by an INSERT. The table
is successfully created with the correct contents.

Regards
David M Bennett FACS

Andl - A New Database Language - andl.org