Return-Path: pg_adm@postgres.berkeley.edu Received: by postgres.Berkeley.EDU (5.61/1.29) id AA26714; Tue, 25 Feb 92 12:59:42 -0800 Date: Tue, 25 Feb 92 12:59:42 -0800 Message-Id: <9202252059.AA26714@postgres.Berkeley.EDU> From: joseash@bush.tamu.edu (Alfredo Sanchez) Subject: Error: No response from the backend, exiting... To: postgres@postgres.berkeley.edu Sender: pg_adm@postgres.berkeley.edu Last week I posted a question regarding this error. I guess I could not make myself clear to get some help, so let me try again. I'll really appreciate (and need) any clue you can come up with. During this time, i've realized that i was trying to run my program from different machines, and that was precluding postgres from using effectively its shared memory mechanism. so i tought that was the origin of all my problems. however, when i shifted to run (only) 2 copies of it in the same machine, the problem persists. this time the results are somewhat different. sometimes it works perfectly, allowing more than 1 program to access the db. other times, one program works properly and the other exits with the message: Error: No response from the backend, exiting... still other times, one program works and the other exits with the message: NOTICE:Feb 25 14:21:49:I have been signalled by the postmaster. NOTICE:Feb 25 14:21:49:Some backend process has died unexpectedly and possibly NOTICE:Feb 25 14:21:49:corrupted shared memory. The current transaction was NOTICE:Feb 25 14:21:49:aborted, and I am going to exit. Please resend the NOTICE:Feb 25 14:21:49:last query. -- The postgres backend NOTICE:Feb 25 14:21:49:last query. -- The postgres backend NOTICE:Feb 25 14:21:49:last query. -- The postgres backend ... and it goes on within an infinite loop. Am I doing the correct assumptions on the pg locking capabilities? I mean, i would expect one program to wait for the other to finish its transaction before proceeding to use the involved classes. I am including a more complete copy of my program below (I just omitted all checking done after pg commands). I'm not asking anyone to follow it, but perhaps you can detect anything wrong on the general proceeding. Thanks for any help you can provide. J Alfredo Sanchez H ------------------- Hypertext Research Lab Department of Computer Science Texas A&M University program. ________________________________________________________ typedef struct { XltIDType appid; XltIDType compid; XltIDType psid; } XltLSTripleType; /* struct def above should be taken from this source file: #include "/home2/Xlt11/source/IPC/XltIPCDefs.h" */ void Browse (pfrom_triple, hostid, pnumtriples, pto_triples, rc) XltLSTripleType *pfrom_triple; /* ORIGIN OF THE LINK TO FOLLOW */ char hostid[16]; /* NAME OF HOST REQUESTING BROWSING OP*/ unsigned *pnumtriples; /* NUMBER OF DESTINATION TRIPLES FOUND*/ XltLSTripleType **pto_triples; /* DESTINATION TRIPLES FOUND*/ XltRCType *rc; /* RETURN CODE */ { /* LOCAL VARIABLES */ char postquery[1024]; /* STORES QUERIES SUBMITTED TO POSTGRES */ PortalBuffer *portalbuff; /* POINTS TO DATA RETRIEVED FROM DB */ char result[512]; /* STORES RESULTS FROM PG OPERATIONS */ unsigned index; /* SUBSCRIPT FOR ARRAY OPERATIONS */ XltRCType lrc; /* RETURN CODE FROM DIAGNOSTIC FUNCTIONS */ XltAddDiagDevice (stderr, "XltFollowLink:", XltDiagEmitXltSevereWarn, &lrc); /* SET DEFAULT RETURN CODE TO OK */ *rc = OK; /* DIRECT POSTQUEL QUERIES TO THE DATABASE CURRENTLY BEING USED */ PQsetdb(XltOM_DB); /* START POSTQUEL TRANSACTION */ strcpy(result,PQexec("begin")); /* GET SIDES IN WHICH GIVEN TRIPLE PARTICIPATES */ sprintf(postquery,"retrieve into temp1_%s (e1.sid) \ from e1 in %s_SIDES \ where e1.appid = \"%ld\" and \ e1.compid = \"%ld\" and \ e1.psid = \"%ld\"", hostid, XltASM_Context, pfrom_triple->appid, pfrom_triple->compid, pfrom_triple->psid); strcpy(result, PQexec(postquery)); /* GET ASSOCIATIONS IN WHICH RESULTING SIDES PARTICIPATE */ sprintf(postquery,"retrieve into temp2_%s (e2.associd) \ from e1 in temp1_%s, \ e2 in %s_ASSOCS \ where e1.sid = e2.sid", hostid, hostid, XltASM_Context); strcpy(result, PQexec(postquery)); /* GET THE OTHER SIDES PARTICIPATING IN RESULTING ASSOCIATIONS */ sprintf(postquery,"retrieve into temp3_%s (e3.sid) \ from e1 in temp1_%s, e2 in temp2_%s, e3 in %s_ASSOCS \ where e3.associd = e2.associd \ and e3.sid != e1.sid", hostid, hostid, hostid, XltASM_Context); strcpy(result, PQexec(postquery)); /* GET LINKED TRIPLES */ sprintf(postquery, "retrieve portal p1 unique (e1.appid,e1.compid,e1.psid) \ from e1 in %s_SIDES, e3 in temp3_%s \ where e1.sid = e3.sid ", XltASM_Context,hostid); strcpy(result, PQexec(postquery)); if (result[0] != 'C') { *rc = PG_FAILED; XltEmitDiag (XltDiagXltSevereWarn,&lrc,"Can't retrieve triples\n"); return; } strcpy(result, PQexec("fetch all in p1")); portalbuff = PQparray("p1"); *pnumtriples = PQntuples(portalbuff); /* ALLOCATE SPACE FOR TRIPLES AND MOVE THEM THERE */ (*pto_triples) = (XltLSTripleType *)palloc(*pnumtriples * sizeof(XltLSTripleType)); for (index = 0; index < *pnumtriples; index++) { (*pto_triples)[index].appid = atoi(PQgetvalue(portalbuff,index,0)); (*pto_triples)[index].compid = atoi(PQgetvalue(portalbuff,index,1)); *pto_triples)[index].psid = atoi(PQgetvalue(portalbuff,index,2)); } /* CLOSE PORTAL */ strcpy(result,PQexec("close p1")); /* DELETE TEMPORARILY CREATED CLASSES */ sprintf(postquery,"destroy temp1_%s",hostid); strcpy(result,PQexec(postquery)); sprintf(postquery,"destroy temp2_%s",hostid); strcpy(result,PQexec(postquery)); sprintf(postquery,"destroy temp3_%s",hostid); strcpy(result,PQexec(postquery)); /* END POSTQUEL TRANSACTION */ strcpy(result,PQexec("end")); /* TERMINATE COMMUNICATIONS WITH BACKEND */ PQfinish(); } main (argc, argv) int argc; char *argv[]; { unsigned long rc; XltLSTripleType from_triple; char hostid[8]; XltLSTripleType *to_triples; unsigned numtriples; unsigned i; strcpy(hostid, *++argv); strcpy(XltASM_Context,"context1"); from_triple.appid = 80; from_triple.compid = 90; from_triple.psid = 100; Browse (&from_triple, hostid, &numtriples, &to_triples, &rc); printf("Got %d triples:\n",numtriples); for (i=0; i