Questions tagged [c]
Questions concerning the C programming language as used in conjunction with database servers. For example writing User Defined Functions in C for Oracle (or other servers). Topics such as writing extensions for PostgreSQL in C would also be relevant. Non-database related C questions should be directed to StackOveflow.
14
questions
2
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Environment variables in Postgres C extension
I cannot get environment variable in my PostgreSQL C extension code.
For example, this function always returns 111:
#include "postgres.h"
#include "fmgr.h"
#include <stdlib.h>...
- 35
0
votes
1
answer
66
views
Postgres C API: How can we copy a Datum?
As far as I understand, SPI_getbinval returns a pointer into the passed row. That is, the following would be unsafe:
dat = SPI_getbinval(SPI_tuptable->vals[0], SPI_tuptable->tupdesc, 1, &...
- 63
1
vote
1
answer
1k
views
What is the difference between RETURNS `SETOF integer` and RETURNS TABLE(name int)`?
Given the two definitions below, is there any difference?
CREATE FUNCTION foo(OUT foobar int4)
RETURNS SETOF int4
AS 'MODULE_PATHNAME', 'foo'
LANGUAGE C STRICT VOLATILE;
And,
CREATE FUNCTION foo()
...
- 58.9k
0
votes
1
answer
57
views
In what circumstance is Materialize_Random set in allowedMode?
In PostgreSQL there is a field called allowedMode called SFRM_Materialize_Random
The Tuplestore must be created with randomAccess = true if
SFRM_Materialize_Random is set in allowedModes, but it can (...
- 58.9k
0
votes
1
answer
50
views
Is there a way to a maintain the function signature in C and not in a SQL file?
Currently the docs says,
There are two ways you can build a composite data value (henceforth a “tuple”): you can build it from an array of Datum values, or from an array of C strings that can be ...
- 58.9k
0
votes
1
answer
17
views
Does PostgreSQL provide anything to dump fcinfo?
I'm looking to get into writing extension in C. I want to better understand what this argument is and how they get changed in different invocations. Is there anything that can dump this argument out ...
- 58.9k
0
votes
1
answer
172
views
What arguments get passed with PG_FUNCTION_ARGS (with the V1 convention)?
PostgreSQL Documents all their C functions with a "V1" interface, but they don't actually show what they get,
PG_FUNCTION_INFO_V1(add_one);
Datum
add_one(PG_FUNCTION_ARGS)
{
int32 arg ...
- 58.9k
0
votes
1
answer
88
views
What is SFRM_Materialize_Preferred and how can it be used to write more performant functions?
Researching this question, I see there is a value for SetFunctionReturnMode called SFRM_Materialize_Preferred. What is this? Can this be used to write more performant functions?
There are multiple ...
- 58.9k
0
votes
1
answer
137
views
C Extension: Is it faster to return a set with ValuePerCall or Materialize mode?
PostgreSQL documents it's Set Returning Functions with C extensions like this,
C-language functions have two options for returning sets (multiple rows).
In one method, called ValuePerCall mode, a ...
- 58.9k
1
vote
2
answers
367
views
Is there a method to print/debug from within a C function in PostgreSQL?
When you're extending PostgreSQL in C, how does one introspect/debug/dump a variable? Is there a method other than returning a custom result set to the client? Something like a printf that I can ...
- 58.9k
0
votes
1
answer
118
views
Remote PostgreSQL DB with local buffer ... how could it look like
I have a sensor which is generating a data vector let's say every second (adjustable to up to 100 vectors per second) at a remote location. The location got 4G modem to send the data. Due to power ...
0
votes
1
answer
791
views
I am getting this error : "Error 102 : non-boolean type specified in a context where a condition is expected" for this request : [closed]
private void button2_Click(object sender, EventArgs e)
{
con.Open();
SqlCommand cmd = con.CreateCommand();
cmd.CommandType = CommandType.Text;
cmd.CommandText = "delete from MYDB ...
- 1
1
vote
1
answer
62
views
MySQL Server :: My C Code can remotely create a database, but not "INSERT INTO" it
I’ve written a C program which does the following when it starts:
Connects to a remote Linux MySQL server over the network
Creates a new, uniquely-named database
Sends a “USE _____” command to ...
- 111
1
vote
0
answers
83
views
How to read jsonb or json in postgresql spi?
How can I read a json/jsonb field in a PostgreSQL server side function?
I am trying to write a server side function using C and SPI for PostgreSQL 11. The json field in mind is simple and contain ...
- 3,105