In a PL language it's sometimes desirable to prevent execution of some
commands. I would like to prevent the commands "begin [work or
transaction]", "commit", and "rollback", completely and I would like to
force the user to use explicit methods for the savepoint methods.

I wonder if there's any way to extract the nature of a command from the
execution plan returned by SPI_prepare. If not, would it be very
difficult to add? It doesn't feel optimal to add a home brewed parser
that parses the statements prior to prepare just to find out if I they
should prevented.

One approach could be to extend the CmdType enum. Perhaps something like
this:

typedef enum CmdType
{
CMD_UNKNOWN,
CMD_SELECT, /* select stmt (formerly retrieve) */
CMD_UPDATE, /* update stmt (formerly replace) */
CMD_INSERT, /* insert stmt (formerly append) */
CMD_DELETE,
CMD_TRANSACTION, /* begin, commit, rollback */
CMD_SAVEPOINT, /* savepoint, rollback to savepoint, release
savepoint */
CMD_UTILITY, /* cmds like create, destroy, copy,
* vacuum, etc. */
CMD_NOTHING /* dummy command for instead nothing
rules
* with qual */
} CmdType;

and then add a SPI function

CmdType SPI_get_command_type(void* executionPlan)

What do you think? It would certanly help PL/Java add safe and efficient
savepoint management and the other PL's are likely to share my concerns.

Regards,
Thomas Hallgren



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Thomas Hallgren <thhal (AT) mailblocks (DOT) com> writes:
If you are executing through SPI then those operations are disallowed
already.

The main problem with this proposal is the erroneous assumption that
there can be only one command in a SPI plan.

regards, tom lane

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On Sun, 2004-11-21 at 16:55 +0100, Thomas Hallgren wrote:
I implemented my own SPI; not for this purpose, but I could [may] use it
for that.
This, of course, would also allow mapping specific utility commands to
my internal methods; instead of inhibiting them (tho, I don't do this
[yet, perhaps]).

[I see Tom's reply, but considering I already wrote this; here it is
anyways.]

Hrm, I can't help but think it would be better just to allow
fetching/access to the Node tag, (e.g. T_TransactionStmt) as opposed to
creating a new command type.

NodeTag SPI_get_utility_tag(void *execPlan);

Well, something like that. I suppose it would somehow need to handle
compound queries.

Perhaps a filter operation would be a better idea.
Passing a function pointer like:

bool (*SPI_UtilityFilter) (NodeTag aStmt);
To a "void SPI_FilterUtilities(void *execPlan, SPI_UtilityFilter fp)".

Throwing an error if deemed necessary by the pointed to function.

Although, I'm inclined to think that if you require this sort of
flexibility you should probably think about writing your own SPI.


While a ways from complete/stable, my Python "SPI":
http://gborg.postgresql.org/project/...query.c?r=HEAD
http://gborg.postgresql.org/project/...ortal.c?r=HEAD

--
Regards,
James William Pye

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James William Pye wrote:

PostgreSQL SPI. That way, all PL's will benefit. That's the reason I
submitted the SPI_is_cursor_plan, SPI_getargtypeid, and SPI_getargcount
functions.

Regards,
Thomas Hallgren




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