Calling db2ReadLog from external UDF - db2

Question

When trying to get transaction log information on a DB2 LUW database through an external UDF calling db2ReadLog a SQL0487N (attempted to execute on SQL statement) is returned. Using the same shared library as a stored procedure works without error.
The reason it needs to be a UDF is to be able to eventually create a table valued UDF which will return actual entries from the transaction log.
Here is the C source for the UDF to determine the initial LRI:
#include <sqlca.h>
#include <db2ApiDf.h>
#include <sqludf.h>
#include <string.h>
#include <stdio.h>
#include <inttypes.h>
#ifdef __plusplus
extern "C"
#endif
SQL_API_RC SQL_API_FN get_initial_lri(SQLUDF_CHAR *lri, SQLUDF_NULLIND
*lri_null_ind, SQLUDF_TRAIL_ARGS)
{
struct sqlca sqlca;
db2ReadLogStruct read_log_params;
db2ReadLogInfoStruct info;
SQL_API_RC rc;
char state_msg[1024], error_msg[1024];
memset(&sqlca, 0, sizeof sqlca);
memset(&read_log_params, 0, sizeof read_log_params);
memset(&info, 0, sizeof info);
read_log_params.iCallerAction = DB2READLOG_QUERY;
read_log_params.iFilterOption = DB2READLOG_FILTER_OFF;
read_log_params.poReadLogInfo = &info;
rc = db2ReadLog(db2Version1058, &read_log_params, &sqlca);
if (rc < 0) {
memcpy(SQLUDF_STATE, "38TA0", SQLUDF_SQLSTATE_LEN);
strncpy(SQLUDF_MSGTX, "Could not query log for initial LRI", SQLUDF_MSGTEXT_LEN);
goto error;
} else if (sqlca.sqlcode < 0) {
strncpy(SQLUDF_STATE, sqlca.sqlstate, SQLUDF_SQLSTATE_LEN);
SQLUDF_MSGTX[0] = '\0';
rc = sqlaintp(error_msg, sizeof error_msg, 80, &sqlca);
if (rc > 0) {
strncpy(SQLUDF_MSGTX, error_msg, SQLUDF_MSGTEXT_LEN);
}
strncat(SQLUDF_MSGTX, "|", SQLUDF_MSGTEXT_LEN);
rc = sqlogstt(state_msg, sizeof state_msg, 80, sqlca.sqlstate);
if (rc > 0) {
strncat(SQLUDF_MSGTX, state_msg, SQLUDF_MSGTEXT_LEN);
}
goto error;
} else {
snprintf(lri, 101, "%" PRIx64 ":%" PRIx64 ":%" PRIx64, info.nextStartLRI.lriType, info.nextStartLRI.part1, info.nextStartLRI.part2);
}
return 0;
error:
return SQLZ_DISCONNECT_PROC;
}
The following SQL is used for registering the C function as an external UDF:
create or replace function get_initial_lri()
returns varchar(100)
language c
external name 'get_initial_lri_0!get_initial_lri'
parameter style sql
fenced not threadsafe
reads sql data
no external action
no scratchpad
no final call
disallow parallel
no dbinfo
And for registering the same code as a stored procedure the SQL is:
create or replace procedure get_initial_lri_sp(out lri varchar(100))
language c
dynamic result sets 0
reads sql data
not deterministic
external name 'get_initial_lri_0!get_initial_lri'
fenced not threadsafe
no external action
program type sub
no dbinfo
parameter style sql
The C source code was compiled with:
gcc -o get_initial_lri_0 get_initial_lri.c -L ~/sqllib/lib64 -ldb2 -shared -fpic -D_REENTRANT -I ~/sqllib/include
The version of DB2 is v10.5.0.8.
Is it at all possible to call the db2ReadLog API from a user defined function?

Answer 1

The documentation states that "connection level APIs cannot be called from within external functions or external methods". And the db2ReadLog API requires a connection. The documentation link is here.
There is another API called db2ReadLogNoconn, maybe you should try that to compare its behaviour, although it may be subject to a different restriction. It is documented here.
Otherwise, a non-external UDF can call a stored procedure (subject to some restrictions) so you may be able to wrap the stored procedure, maybe you can investigate.