Encounter ORA-01002 when calling OCIStmtFetch2 to fetch blob data

Question

Oracle Version：Release 10.2.0.1.0
Description:
We use these two functions to fetch the content of blob field dynamically in batch mode:
OCIDefineByPos(OCI_DYNAMIC_FETCH)
OCIDefineDynamic(callbackfun->cbf_get_data)
We allocate fixed memory to fetch data in order to using compact memory.
If the size of blob to be fetched is larger than the allocated memory size, the fetch can not be done in one call, which need to be interrupted.
Those records would remain in cache and can only be fetched until calling OCIStmtFetch2 next time.
The callback function:cbf_get_data, achieves this by returning OCI_ROWCBK_DONE, which marks current fetch interrupted.
It would not return OCI_CONTINUE, because OCI_CONTINUE can not interrupt current fetch procedure in time.
We made a sample code test, and found this logic only works when fetching small rows (nearly 800 rows). Exceptions occurred when fetching more rows(>=1000 rows).
For example, among these 2 cases,
1.（OCIStmtFetch2(m_stmthp,m_errhp,(ub4)800,OCI_FETCH_NEXT,(sb4)OCI_FETCH_RELATIVE,OCI_DEFAULT)
2.（OCIStmtFetch2(m_stmthp,m_errhp,(ub4)1000,OCI_FETCH_NEXT,(sb4)OCI_FETCH_RELATIVE,OCI_DEFAULT)
only the 1st one work, but the 2nd.
After function cbf_get_data returns OCI_ROWCBK_DONE, calling OCIStmtFetch2 did not enter into callback function cbf_get_data.
And OCIErrorGet showed such error:
ORA-01002: fetch out of sequence
the total number of result set is about 100,000.
We tried to set PREFETCH to a larger value in this way::
OCIAttrSet(m_stmthp,OCI_HTYPE_STMT,(dvoid *)&rnum,0,OCI_ATTR_PREFETCH_ROWS,m_errhp);
rtn=OCIAttrSet((dvoid *)m_stmthp, (ub4) OCI_HTYPE_STMT,(dvoid *)&preFetch, (ub4)sizeof(preFetch), OCI_ATTR_PREFETCH_MEMORY,m_errhp);
but it did not help.
Waiting for you guidance.
Thanks in advance!
-Andy
Edited by: Andy Tong on 2010-10-22 上午12:29

Answer 1

Here is our testing Code：
#include "oci.h"
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#pragma comment(lib,"oci.lib")
char buf1[5000];
char buf2[5000];
long datalen=5000;
ub4 outpos=1;
ub4 outpos2=2;
int sum=0;
int sum2=0;
OCIError *m_errhp;
OCIStmt *m_stmthp;
char      LOBBuf[8006];
long      LOBLen=8006;
long     gindpp=0;
ub2     grcpp=0;
#define MAX_ROW_NUM 56338
/* Fetch callback to specify buffers. */
sb4 cbf_get_data(     dvoid*          ctxp,
                         OCIDefine*     dfnhp,
                         ub4               iter,
                         dvoid**          bufpp,
                         ub4**          alenpp,
                         ub1*          piecep,
                         dvoid**          indpp,
                         ub2**          rcpp)
     if(iter==0)
          sum=0;
     else if(iter>=858) //857 exception
          //LOBBuf,LOBLen
          //     sum+=LOBLen;
          //     if(sum>1057552-100*1024)
          sum=0;
          bufpp=(dvoid)0;
          alenpp=(ub4)0;
          *piecep = (ub1)OCI_ONE_PIECE;
          indpp = (dvoid ) 0;
          rcpp     = (ub2 ) 0;
          return(OCI_ROWCBK_DONE);     
     LOBLen=8006;
     bufpp=(dvoid)LOBBuf;
     alenpp=(ub4)&LOBLen;
     *piecep = (ub1)OCI_ONE_PIECE;
     indpp = (dvoid )&gindpp;
     rcpp     = (ub2 )&grcpp;
     return(OCI_CONTINUE);     
BOOL CTest_ociApp::InitInstance()
     OCIEnv *          m_envhp;
     OCIServer *          m_srvhp;
     OCISvcCtx *          m_svchp;
     sword               rtn;
     char               sqlState[256];
     int               nativeErr;
     char               errTxt[256];
     unsigned long          bufLen=256;
     OCIDefine hDefine =  (OCIDefine ) 0;
     OCIDefine hDefine1 = (OCIDefine ) 0;
     OCIDefine hDefine2 = (OCIDefine ) 0;
     OCIDefine hDefine3 = (OCIDefine ) 0;
     OCIDefine hDefine4 = (OCIDefine ) 0;
     int i;
     OCILobLocator** lob_array;
     char username[255];
     char password[30];
     char dbname[30];
     char szSqlStr[255];
     ub4 preFetch= 10*1024*16;
     strcpy(username,"dlg25w");
     strcpy(password,"sa");
     strcpy(dbname,"WIN10G");
     OCIEnvCreate(&m_envhp, OCI_DEFAULT | OCI_OBJECT, 0, 0, 0, 0, 0, 0);
     OCIHandleAlloc( (dvoid *)m_envhp, (dvoid **)&m_errhp,OCI_HTYPE_ERROR,(size_t) 0, (dvoid **) 0);
     OCIHandleAlloc( (dvoid *)m_envhp, (dvoid **)&m_srvhp,OCI_HTYPE_SERVER,(size_t) 0, (dvoid **) 0);
     OCIHandleAlloc( (dvoid *)m_envhp, (dvoid **)&m_svchp,OCI_HTYPE_SVCCTX,(size_t) 0, (dvoid **) 0);
     OCIHandleAlloc( (dvoid *)m_envhp, (dvoid **)&m_stmthp,OCI_HTYPE_STMT,(size_t) 0, (dvoid **)0);
     OCIServerAttach(m_srvhp, m_errhp,(text *)dbname, strlen(dbname),(ub4) OCI_DEFAULT);
     OCILogon(m_envhp,m_errhp,&m_svchp,(text *)username,strlen(username),(text *)password,strlen(password),(text *)dbname,strlen(dbname));
     ub4     rnum=0;
     unsigned int len=0;
     //rtn=OCIAttrGet(m_envhp,OCI_HTYPE_ENV,(dvoid *)&rnum,&len,OCI_ATTR_CACHE_MAX_SIZE,m_errhp);
     OCIErrorGet((dvoid *) m_errhp,(ub4)1,(OraText *)sqlState,&nativeErr,(unsigned char*)errTxt,bufLen,(ub4) OCI_HTYPE_ERROR);
     len=4;
     rnum=83886080;
     rtn=OCIAttrSet(m_envhp,OCI_HTYPE_ENV,(dvoid *)&rnum,len,OCI_ATTR_CACHE_OPT_SIZE,m_errhp);
     rtn=OCIAttrGet(m_envhp,OCI_HTYPE_ENV,(dvoid *)&rnum,&len,OCI_ATTR_CACHE_OPT_SIZE,m_errhp);
     OCIErrorGet((dvoid *) m_errhp,(ub4)1,(OraText *)sqlState,&nativeErr,(unsigned char*)errTxt,bufLen,(ub4) OCI_HTYPE_ERROR);
     rnum=2000;
     sprintf( szSqlStr,"%s", "SELECT DATA FROM MF4");
     OCIStmtPrepare(m_stmthp, m_errhp, (text*)szSqlStr, (ub4)strlen(szSqlStr),(ub4) OCI_NTV_SYNTAX, (ub4)OCI_DEFAULT);
OCIAttrSet(m_stmthp,OCI_HTYPE_STMT,(dvoid *)&rnum,0,OCI_ATTR_PREFETCH_ROWS,m_errhp);
     /* initialize array of locators */
     OCIDefineByPos(m_stmthp, &hDefine2, m_errhp, (ub4)1,(dvoid *)0,(sb4)8006,SQLT_BIN,(dvoid *)0, (ub2 *)0, (ub2 *)0,(ub4) OCI_DYNAMIC_FETCH);//OCI_DYNAMIC_FETCH
     OCIDefineDynamic(hDefine2, m_errhp, (dvoid *)&outpos,(OCICallbackDefine)cbf_get_data);
     OCIStmtExecute(m_svchp, m_stmthp, m_errhp,(ub4)0, (ub4) 0,(const OCISnapshot*) 0,
          (OCISnapshot*)0,(ub4)OCI_DEFAULT);//OCI_STMT_SCROLLABLE_READONLY
     rtn=OCIAttrSet((dvoid *)m_stmthp, (ub4) OCI_HTYPE_STMT,(dvoid *)&preFetch, (ub4)sizeof(preFetch), OCI_ATTR_PREFETCH_MEMORY,m_errhp);
     while(1)
          rtn=OCIStmtFetch2(m_stmthp,m_errhp,(ub4)1000,OCI_FETCH_NEXT,(sb4)OCI_FETCH_RELATIVE,OCI_DEFAULT);
          OCIErrorGet((dvoid *) m_errhp,(ub4)1,(OraText *)sqlState,&nativeErr,(unsigned char*)errTxt,bufLen,(ub4) OCI_HTYPE_ERROR);
          if(rtn==OCI_NO_DATA)
               break;
          else
     t0=GetTickCount()-t0;
     t0=0;
     OCIAttrGet((CONST void *)m_stmthp,OCI_HTYPE_STMT,(void *)&rows_fetched,(ub4 *)sizeof(rows_fetched),OCI_ATTR_ROW_COUNT ,m_errhp);
     printf("\n Total number of records：%d",rows_fetched);
     OCILogoff( m_svchp, m_errhp );
     OCIServerDetach( m_srvhp, m_errhp, OCI_DEFAULT );
     OCIHandleFree((dvoid *) m_stmthp, OCI_HTYPE_STMT);
     OCIHandleFree((dvoid *) m_svchp, OCI_HTYPE_SVCCTX);
     OCIHandleFree((dvoid *) m_srvhp, OCI_HTYPE_SERVER);
     OCIHandleFree((dvoid *) m_errhp, OCI_HTYPE_ERROR);
     getchar();
     return FALSE;
}