Click here to view and discuss this page in DocCommentXchange. In the future, you will be sent there automatically.

SQL Anywhere 11.0.0 » SQL Anywhere Server - Programming » SQL Anywhere Data Access APIs » SQL Anywhere external environment support

 

The ESQL and ODBC external environments

SQL Anywhere has had the ability to call compiled native functions written in C or C++ for some time. However, when these procedures are run by the database server, the dynamic link library or shared object has always been loaded by the database server and the calls out to the native functions have always been made by the database server. While having the database server make these native calls is most efficient, there can be serious consequences if the native function misbehaves. In particular, if the native function enters an infinite loop, then the database server can hang, and if the native function causes a fault, then the database server crashes. As a result, you now have the option of running compiled native functions outside of the database server, in an external environment. There are some key benefits to running a compiled native function in an external environment:

  1. The database server does not hang or crash if the compiled native function misbehaves.
  2. The native function can be written as either an ESQL or an ODBC application and can make server-side calls back into the database server without having to make a connection.
  3. The native function can return a result set to the database server.
  4. In the external environment, a 32-bit database server can communicate with a 64-bit compiled native function and vice versa. Note that this is not possible when the compiled native functions are loaded directly into the address space of the database server. A 32-bit library can only be loaded by a 32-bit server and a 64-bit library can only be loaded by a 64-bit server.

It should be noted, though, that running a compiled native function in an external environment instead of within the database server results in a small performance penalty.

It should also be noted that the compiled native function must use the native function call API. This API is described in SQL Anywhere External Function API.

To run a compiled native C function in an external environment instead of within the database server, the stored procedure or function is defined with the EXTERNAL NAME clause followed by the LANGUAGE clause specifying one of C_ESQL32, C_ESQL64, C_ODBC32, or C_ODBC64.

Unlike the Perl, PHP, and Java external environments, the ESQL and ODBC environments do not have anything installed in the database. As a result, you do not need to execute any INSTALL statements prior to using the ESQL and ODBC external environments.

Here is an example of a function written in C++ that can be run within the database server or in an external environment.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <windows.h>
#include "extfnapi.h"
    
BOOL APIENTRY DllMain( HMODULE hModule,
    DWORD  ul_reason_for_call,
    LPVOID lpReserved
    )
{
    return TRUE;
}

// Note: extfn_use_new_api used only for
// execution in the database server

extern "C" __declspec( dllexport )
a_sql_uint32 extfn_use_new_api( void )
{
    return( EXTFN_API_VERSION );
}
    
extern "C" __declspec( dllexport )
void SimpleCFunction(
    an_extfn_api *api,
    void *arg_handle )
{
    short               result;
    an_extfn_value      arg;
    an_extfn_value      retval;
    int *               intp;
    int                 i, j, k;
    
    j = 1000;
    k = 0;
    for( i = 1; i <= 4; i++ )
    {
        result = api->get_value( arg_handle, i, &arg );
        if( result == 0 || arg.data == NULL ) break;
        if( arg.type & DT_TYPES != DT_INT ) break;
        intp = (int *) arg.data;
        k += *intp * j;
        j = j / 10;
    }
    retval.type = DT_INT;
    retval.data = (void*)&k;
    retval.piece_len = retval.len.total_len = 
       (a_sql_uint32) sizeof( int );
    api->set_value( arg_handle, 0, &retval, 0 );    
    return;
}

When compiled into a dynamic link library or shared object, this function can be called from an external environment. An executable image called dbexternc11 is started by the database server and this executable image loads the dynamic link library for you. Different versions of this executable are included with SQL Anywhere. For example, on Windows you may have both 32-bit and 64-bit executables.

Note that 32-bit or 64-bit versions of the database server can be used and either version can start 32-bit or 64-bit versions of dbexternc11. This is one of the advantages of using the external environment. Note that once dbexternc11 is started by the database server, it does not terminate until the connection has been terminated.

In order to call the compiled native function, SimpleCFunction, a wrapper is defined as follows:

CREATE FUNCTION SimpleCDemo( 
  IN arg1 INT, 
  IN arg2 INT, 
  IN arg3 INT, 
  IN arg4 INT )
RETURNS INT
EXTERNAL NAME 'SimpleCFunction@d:\\c\\extdemo.dll' 
LANGUAGE C_ODBC32;

This is almost identical to the way a compiled native function is described when it is to be loaded into the database server's address space. The one difference is the use of the LANGUAGE C_ODBC32 clause. This clause indicates that SimpleCDemo is a function running in an external environment and that it is using 32-bit ODBC calls.

To execute the sample compiled native function, execute the following statement.

SELECT SimpleCDemo(1,2,3,4);

The language specification of C_ESQL32, C_ESQL64, C_ODBC32, or C_ODBC64 tells the database server whether the external C function issues 32-bit or 64-bit embedded SQL or ODBC calls when making server-side requests. If the function does not make any server-side requests, then either the ESQL or ODBC specification will do. For more information on how to make server-side requests and how to return result sets from an external C function, refer to the samples in samples-dir\SQLAnywhere\ExternalEnvironments\ExternC.

To use server-side ODBC, the C/C++ code must use the default database connection. To get a handle to the database connection, call get_value with an EXTFN_CONNECTION_HANDLE_ARG_NUM argument. The argument tells the database server to return the current external environment connection rather than opening a new one.

#include <windows.h>
#include <stdio.h>
#include "odbc.h"
#include "extfnapi.h"
    
BOOL APIENTRY DllMain( HMODULE hModule,
    DWORD  ul_reason_for_call,
    LPVOID lpReserved
    )
{
    return TRUE;
}
    
extern "C" __declspec( dllexport ) 
void ServerSideFunction( an_extfn_api *api, void *arg_handle )
{
    short               result;
    an_extfn_value      arg;
    an_extfn_value      retval;
    SQLRETURN           ret;

    ret = -1;
    // set up the return value struct
    retval.type = DT_INT;
    retval.data = (void*) &ret;
    retval.piece_len = retval.len.total_len =
        (a_sql_uint32) sizeof( int );

    result = api->get_value( arg_handle,
                    EXTFN_CONNECTION_HANDLE_ARG_NUM,
                    &arg );
    if( result == 0 || arg.data == NULL )
    {
        api->set_value( arg_handle, 0, &retval, 0 );
        return;
    }

    HDBC dbc = (HDBC)arg.data;
    HSTMT stmt = SQL_NULL_HSTMT;
    ret = SQLAllocHandle( SQL_HANDLE_STMT, dbc, &stmt );
    if( ret != SQL_SUCCESS ) return;
    ret = SQLExecDirect( stmt,
            (SQLCHAR *) "INSERT INTO odbcTab "
                "SELECT table_id, table_name "
                "FROM SYS.SYSTAB", SQL_NTS );
    if( ret == SQL_SUCCESS )
    {
        SQLExecDirect( stmt,
            (SQLCHAR *) "COMMIT", SQL_NTS );
    }
    SQLFreeHandle( SQL_HANDLE_STMT, stmt );
    
    api->set_value( arg_handle, 0, &retval, 0 );
    return;
}

If the above ODBC code is stored in the file extodbc.cpp, it can be built for Windows using the following commands (assuming that the SQL Anywhere software is installed in the folder c:\sa11 and that Microsoft Visual C++ is installed).

cl extodbc.cpp /LD /Ic:\sa11\sdk\include odbc32.lib

The following example creates a table, defines the stored procedure wrapper to call the compiled native function, and then calls the native function to populate the table.

CREATE TABLE odbcTab(c1 int, c2 char(128));

CREATE FUNCTION ServerSideODBC( )
RETURNS INT
EXTERNAL NAME 'ServerSideFunction@extodbc.dll'
LANGUAGE C_ODBC32;

SELECT ServerSideODBC();

// The following statement should return two identical rows
SELECT COUNT(*) FROM odbcTab 
UNION ALL 
SELECT COUNT(*) FROM SYS.SYSTAB;

Similarly, to use server-side ESQL, the C/C++ code must use the default database connection. To get a handle to the database connection, call get_value with an EXTFN_CONNECTION_HANDLE_ARG_NUM argument. The argument tells the database server to return the current external environment connection rather than opening a new one.

#include <windows.h>
#include <stdio.h>

#include "sqlca.h"
#include "sqlda.h"
#include "extfnapi.h"

BOOL APIENTRY DllMain( HMODULE hModule,
    DWORD  ul_reason_for_call,
    LPVOID lpReserved
    )
{
    return TRUE;
}

EXEC SQL INCLUDE SQLCA;
static SQLCA *_sqlc;
EXEC SQL SET SQLCA "_sqlc";
EXEC SQL WHENEVER SQLERROR { ret = _sqlc->sqlcode; };

extern "C" __declspec( dllexport ) 
void ServerSideFunction( an_extfn_api *api, void *arg_handle )
{
    short               result;
    an_extfn_value      arg;
    an_extfn_value      retval;

    EXEC SQL BEGIN DECLARE SECTION;
    char *stmt_text =
        "INSERT INTO esqlTab "
            "SELECT table_id, table_name "
            "FROM SYS.SYSTAB";
    char *stmt_commit =
        "COMMIT";
    EXEC SQL END DECLARE SECTION;

    int ret = -1;

    // set up the return value struct
    retval.type = DT_INT;
    retval.data = (void*) &ret;
    retval.piece_len = retval.len.total_len =
        (a_sql_uint32) sizeof( int );

    result = api->get_value( arg_handle,
                    EXTFN_CONNECTION_HANDLE_ARG_NUM,
                    &arg );
    if( result == 0 || arg.data == NULL )
    {
        api->set_value( arg_handle, 0, &retval, 0 );
        return;
    }
    ret = 0;
    _sqlc = (SQLCA *)arg.data;

    EXEC SQL EXECUTE IMMEDIATE :stmt_text;
    EXEC SQL EXECUTE IMMEDIATE :stmt_commit;

    api->set_value( arg_handle, 0, &retval, 0 );
}

If the above embedded SQL code is stored in the file extesql.sqc, it can be built for Windows using the following commands (assuming that the SQL Anywhere software is installed in the folder c:\sa11 and that Microsoft Visual C++ is installed).

sqlpp extesql.sqc extesql.cpp
cl extesql.cpp /LD /Ic:\sa11\sdk\include c:\sa11\sdk\lib\x86\dblibtm.lib

The following example creates a table, defines the stored procedure wrapper to call the compiled native function, and then calls the native function to populate the table.

CREATE TABLE esqlTab(c1 int, c2 char(128));

CREATE FUNCTION ServerSideESQL( )
RETURNS INT
EXTERNAL NAME 'ServerSideFunction@extesql.dll'
LANGUAGE C_ESQL32;

SELECT ServerSideESQL();

// The following statement should return two identical rows
SELECT COUNT(*) FROM esqlTab 
UNION ALL 
SELECT COUNT(*) FROM SYS.SYSTAB;

For additional information, see SQL Anywhere External Function API.