TL;DR
One has to compile their custom library as shared library:
gcc -c -fPIC warp_client.c -o warp_client.o
gcc -shared warp_client.o libwarp-client.so
Include the shared library and additional dependencies of that shared library in the Postgresql Makefile with the flags SHLIB_LINK and PG_LDFLAGS(Here the bachelor_fdw.c is the extension to compile):
EXTENSION = bachelor_fdw
MODULE_big = bachelor_fdw
DATA = bachelor_fdw--0.1.sql
OBJS = bachelor_fdw.o
PG_LIBS = -lpq
SHLIB_LINK = -lwarp_client -lucp
PG_LDFLAGS += -L/usr/lib/warpdrive/ -L/usr/lib/ucx/
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)
Include the directories of the shared libraries into the environment variable LD_LIBRARY_PATH of Postgresql. For that, one has to add a line to the file 'environment' in the main Postgresql directory and restart Postgresql. Here is mine:
$ cat /etc/postgresql/12/main/environment
# environment variables for postgres processes
# This file has the same syntax as postgresql.conf:
# VARIABLE = simple_value
# VARIABLE2 = 'any value!'
# I. e. you need to enclose any value which does not only consist of letters,
# numbers, and '-', '_', '.' in single quotes. Shell commands are not
# evaluated.
LD_LIBRARY_PATH='/usr/include/:/usr/include/ucx/:/usr/lib/:/usr/lib/ucx/'
I am trying to create a foreign data wrapper, which uses a custom library from me. The fdw compiles and installs fine, but when using it, symbols to my library are undefined. What is the proper way of using custom c code as library in a postgresql extension and what am i doing wrong? Here are the steps i took:
- Compile my library (warp_client.c) with flag -fPIC into an object file.
gcc -c -fPIC warp_client.c -o static/warp_client.o
- Create static library from the object file.
ar -rcs out/libwarp_client.a static/warp_client.o
- Copy libwarp_client.a and warp_client.h into the postgresql extension project root.
- Compile postgresql extension with the following makefile.
EXTENSION = bachelor_fdw
MODULE_big = bachelor_fdw
DATA = bachelor_fdw--0.1.sql libwarp_client.a
OBJS = bachelor_fdw.o
HEADERS = warp_client.h
ifdef DEBUG
$(info $(shell echo "debug ist an"))
endif
PG_LIBS = -lpq
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)
make USE_PGXS=1 install
- Try to create the extension. The extension makes a call to a library function in it's _PG_INI() function. Error comes up:
CREATE EXTENSION IF NOT EXISTS bachelor_fdw;
psql:only_create.sql:3: ERROR: could not load library "/usr/lib/postgresql/12/lib/bachelor_fdw.so": /usr/lib/postgresql/12/lib/bachelor_fdw.so: undefined symbol: warpclient_getData
The warp_client.h has the function headers and warp_client.c has the functions. warp_client.c includes "warp_client.h", bachelor_fdw.c (the extension) includes "warp_client.h".
warp_client.h:
#ifndef TEST_FIELD_UCP_WARP_CLIENT_H
#define TEST_FIELD_UCP_WARP_CLIENT_H
#include <ucp/api/ucp.h>
int warpclient_queryServer(char *server_addr_local, int port, int useINet6, char *query);
void *warpclient_getData();
int warpclient_cleanup();
#endif //TEST_FIELD_UCP_WARP_CLIENT_H
Any more desired info? I would be really glad for any help.
EDIT 1
I use the functions from warp_client.h inside of bachelor_fdw.c. Do i still need to export them? I thought only functions, which get called from the postgresql server needs to be exported.
Here is part of bachelor_fdw.c:
#include <warp_client.h>
#include "postgres.h"
#include "foreign/fdwapi.h"
#include "foreign/foreign.h"
#include "nodes/nodes.h"
#include "optimizer/pathnode.h"
#include "optimizer/planmain.h"
...
PG_MODULE_MAGIC;
/*
* SQL functions
*/
PG_FUNCTION_INFO_V1(bachelor_fdw_handler);
PG_FUNCTION_INFO_V1(bachelor_fdw_validator);
/*
* Extension initialization functions
*/
extern void _PG_init(void);
extern void _PG_fini(void);
/*
* FDW callback routines
*/
static void bachelorBeginForeignScan(ForeignScanState *node, int eflags);
static TupleTableSlot *bachelorIterateForeignScan(ForeignScanState *node);
static void bachelorReScanForeignScan(ForeignScanState *node);
static void bachelorEndForeignScan(ForeignScanState *node);
static void bachelorGetForeignRelSize(PlannerInfo *root, RelOptInfo *baserel, Oid foreigntableid);
static void bachelorGetForeignPaths(PlannerInfo *root, RelOptInfo *baserel, Oid foreigntableid);
static ForeignScan* bachelorGetForeignPlan(PlannerInfo *root, RelOptInfo *baserel, Oid foreigntableid, ForeignPath *best_path, List *tlist, List *scan_clauses, Plan *outer_plan);
void _PG_init(void){
int ret = 0;
void *data;
ret = warpclient_queryServer(NULL, -1, 0, "SELECT TEST FROM TEST;");
elog_debug("Testquery for server. Return code (%d)...\n", ret);
while(NULL != (data = warpclient_getData())){
elog_debug("Data received as fdw: %s\n", data);
}
elog_debug("Finished receiving data.\n");
/* Call cleanup */
ret = warpclient_cleanup();
elog_debug("Warpclient cleanup (%d)...\n", ret);
}
And here is part of warp_client.c:
#include "warp_client.h"
...
int warpclient_cleanup(){
int ret = 0;
//free buffers
free(recvbuffer->buffer);
free(recvbuffer);
/* Close the endpoint to the server */
debugmsg("Close endpoint.\n");
ep_close();
/* releasing UCX ressources */
ucp_worker_destroy(ucp_worker);
ucp_cleanup(ucp_context);
return ret;
}
int warpclient_queryServer(char *server_addr_local, int port, int useINet6, char *query){
/*
* Initialize important connection variables
*/
debugmsg("Initializing connection variables...\n");
if(NULL != server_addr_local) server_addr = server_addr_local;
if((port >= 0) && (port <= UINT16_MAX)) server_port = port;
if(useINet6) ai_family = AF_INET6;
int ret;
/* Initialize the UCX required objects worker and context*/
debugmsg("Initializing context and worker...\n");
ret = init_context_and_worker();
if (ret != 0) {
fprintf(stderr, "Initializing worker or context failed! Exiting..\n");
return -2;
}
/*
* UCP objects: client_ep as communication endpoint for the worker.
* status for function error code check.
*/
ucs_status_t status;
/* ep initialization and exchange with server over sockets */
debugmsg("Creating Client endpoint.\n");
status = create_client_endpoint();
if (status != UCS_OK) {
fprintf(stderr, "failed to start client (%s)\n", ucs_status_string(status));
return -1;
}
ret = send_query(query);
if(ret!=0){
debugmsg("Failed to connect to Server.\n");
}
return ret;
}
EDIT 2
I managed to get a good step forward thanks to Laurenz Albe. But i still have a problem with a shared library used in my shared library. Do I also need to link to shared libraries used in my own shared library, even though i linked that as i compiled my shared library before distribution?
what I did:
I added SHLIB_LINK = -lwarp_client to the Makefile and also needed the line PG_LDFLAGS += -L. for the linker to find libwarp_client.so.
I also managed to include the environment variable LD_LIBRARY_PATH for the postgres service, so that it can find my library in the standard places. And removed the library from the DATA flag in the Makefile.
New Makefile:
EXTENSION = bachelor_fdw
MODULE_big = bachelor_fdw
DATA = bachelor_fdw--0.1.sql
OBJS = bachelor_fdw.o
ifdef DEBUG
$(info $(shell echo "debug ist an"))
endif
PG_LIBS = -lpq
SHLIB_LINK = -lwarp_client
PG_LDFLAGS += -L.
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)
Enrivonment variables:
/proc/1551/environ | xargs -0 -n 1 echo
LD_LIBRARY_PATH=/usr/include/:/usr/include/ucx/:/usr/lib/:/usr/lib/ucx/
...
When using CREATE on the extension, my library gets used but postgres complains about another shared library, which my library uses.
psql:only_create.sql:3: ERROR: could not load library "/usr/lib/postgresql/12/lib/bachelor_fdw.so": /usr/lib/warpdrive/libwarp_client.so: undefined symbol: ucp_ep_create
The error clearly says, it uses my shared library from a subdirectory "warpdrive" in the included standard directory. The shared library from UCP is also in that standard directory:
ls /usr/lib/ucx
cmake libjucx.so.0.0.0 libucp.a libucs.la libuct.so
jucx-1.12.1.jar libucm.a libucp.la libucs.so libuct.so.0
libjucx.a libucm.la libucp.so libucs.so.0 libuct.so.0.0.0
libjucx.la libucm.so libucp.so.0 libucs.so.0.0.0 pkgconfig
libjucx.so libucm.so.0 libucp.so.0.0.0 libuct.a ucx
libjucx.so.0 libucm.so.0.0.0 libucs.a libuct.la
