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Overview
Comment:Have the sqlite3session_apply() function and its streaming equivalent retry any operations that failed with SQLITE_CONSTRAINT after all other operations on the same table have been attempted. New code is largely untested.
Downloads: Tarball | ZIP archive | SQL archive
Timelines: family | ancestors | descendants | both | session-retry
Files: files | file ages | folders
SHA1: 1085911afb51744f32fe9db183b50e8e88bdd73e
User & Date: dan 2016-03-30 21:19:00
Context
2016-03-31
00:45
Fix the return code in sessionRetryConstraints(). check-in: ea917c14 user: drh tags: session-retry
2016-03-30
21:19
Have the sqlite3session_apply() function and its streaming equivalent retry any operations that failed with SQLITE_CONSTRAINT after all other operations on the same table have been attempted. New code is largely untested. check-in: 1085911a user: dan tags: session-retry
16:23
Updates for the MSVC makefiles. check-in: 7cf0cab7 user: mistachkin tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to ext/session/session1.test.

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  INSERT INTO t1 VALUES(3, 'three');
  INSERT INTO t1 VALUES(4, 'four');
  INSERT INTO t1 VALUES(5, 'five');
  INSERT INTO t1 VALUES(6, 'six');
  INSERT INTO t1 VALUES(7, 'seven');
  INSERT INTO t1 VALUES(8, NULL);
} -conflicts {
  {INSERT t1 CONSTRAINT {i 8 n {}}}
  {INSERT t1 CONFLICT {i 6 t six} {i 6 t VI}}

}

do_db2_test 3.1.3 "SELECT * FROM t1" {
  6 VI 3 three 4 four 5 five 7 seven
}
do_execsql_test 3.1.4 "SELECT * FROM t1" {
  1 one 2 two 3 three 4 four 5 five 6 six 7 seven 8 {}
................................................................................
}
do_conflict_test 3.3.3 -tables t4 -sql {
  UPDATE t4 SET a = -1 WHERE b = 2;
  UPDATE t4 SET a = -1 WHERE b = 5;
  UPDATE t4 SET a = NULL WHERE c = 9;
  UPDATE t4 SET a = 'x' WHERE b = 11;
} -conflicts {
  {UPDATE t4 CONSTRAINT {i 7 i 8 i 9} {n {} {} {} {} {}}}
  {UPDATE t4 DATA {i 1 i 2 i 3} {i -1 {} {} {} {}} {i 0 i 2 i 3}}
  {UPDATE t4 NOTFOUND {i 4 i 5 i 6} {i -1 {} {} {} {}}}

}
do_db2_test     3.3.4 { SELECT * FROM t4 } {0 2 3 4 5 7 7 8 9 x 11 12}
do_execsql_test 3.3.5 { SELECT * FROM t4 } {-1 2 3 -1 5 6 {} 8 9 x 11 12}

#-------------------------------------------------------------------------
# This next block of tests verifies that values returned by the conflict
# handler are intepreted correctly.







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  INSERT INTO t1 VALUES(3, 'three');
  INSERT INTO t1 VALUES(4, 'four');
  INSERT INTO t1 VALUES(5, 'five');
  INSERT INTO t1 VALUES(6, 'six');
  INSERT INTO t1 VALUES(7, 'seven');
  INSERT INTO t1 VALUES(8, NULL);
} -conflicts {

  {INSERT t1 CONFLICT {i 6 t six} {i 6 t VI}}
  {INSERT t1 CONSTRAINT {i 8 n {}}}
}

do_db2_test 3.1.3 "SELECT * FROM t1" {
  6 VI 3 three 4 four 5 five 7 seven
}
do_execsql_test 3.1.4 "SELECT * FROM t1" {
  1 one 2 two 3 three 4 four 5 five 6 six 7 seven 8 {}
................................................................................
}
do_conflict_test 3.3.3 -tables t4 -sql {
  UPDATE t4 SET a = -1 WHERE b = 2;
  UPDATE t4 SET a = -1 WHERE b = 5;
  UPDATE t4 SET a = NULL WHERE c = 9;
  UPDATE t4 SET a = 'x' WHERE b = 11;
} -conflicts {

  {UPDATE t4 DATA {i 1 i 2 i 3} {i -1 {} {} {} {}} {i 0 i 2 i 3}}
  {UPDATE t4 NOTFOUND {i 4 i 5 i 6} {i -1 {} {} {} {}}}
  {UPDATE t4 CONSTRAINT {i 7 i 8 i 9} {n {} {} {} {} {}}}
}
do_db2_test     3.3.4 { SELECT * FROM t4 } {0 2 3 4 5 7 7 8 9 x 11 12}
do_execsql_test 3.3.5 { SELECT * FROM t4 } {-1 2 3 -1 5 6 {} 8 9 x 11 12}

#-------------------------------------------------------------------------
# This next block of tests verifies that values returned by the conflict
# handler are intepreted correctly.

Added ext/session/sessionG.test.





































































































































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# 2016 March 30
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
#
# This file implements regression tests for the sessions module.
# Specifically, it tests that UNIQUE constraints are dealt with correctly.
#



if {![info exists testdir]} {
  set testdir [file join [file dirname [info script]] .. .. test]
} 
source [file join [file dirname [info script]] session_common.tcl]
source $testdir/tester.tcl
ifcapable !session {finish_test; return}
set testprefix sessionG


forcedelete test.db2
sqlite3 db2 test.db2

do_test 1.0 {
  do_common_sql {
    CREATE TABLE t1(a PRIMARY KEY, b UNIQUE);
    INSERT INTO t1 VALUES(1, 'one');
    INSERT INTO t1 VALUES(2, 'two');
    INSERT INTO t1 VALUES(3, 'three');
  }
  do_then_apply_sql {
    DELETE FROM t1 WHERE a=1;
    INSERT INTO t1 VALUES(4, 'one');
  }
  compare_db db db2
} {}

do_test 1.1 {
  do_then_apply_sql {
    DELETE FROM t1 WHERE a=4;
    INSERT INTO t1 VALUES(1, 'one');
  }
  compare_db db db2
} {}

do_test 1.2 {
  execsql { INSERT INTO t1 VALUES(5, 'five') } db2
  do_then_apply_sql {
    INSERT INTO t1 VALUES(11, 'eleven');
    INSERT INTO t1 VALUES(12, 'five');
  }
  execsql { SELECT * FROM t1 } db2
} {2 two 3 three 1 one 5 five 11 eleven}

do_test 1.3 {
  execsql { SELECT * FROM t1 }
} {2 two 3 three 1 one 11 eleven 12 five}

finish_test

Changes to ext/session/sqlite3session.c.

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/*
** An object of this type is used internally as an abstraction for 
** input data. Input data may be supplied either as a single large buffer
** (e.g. sqlite3changeset_start()) or using a stream function (e.g.
**  sqlite3changeset_start_strm()).
*/
struct SessionInput {


  int iNext;                      /* Offset in aData[] of next change */
  u8 *aData;                      /* Pointer to buffer containing changeset */
  int nData;                      /* Number of bytes in aData */

  SessionBuffer buf;              /* Current read buffer */
  int (*xInput)(void*, void*, int*);        /* Input stream call (or NULL) */
  void *pIn;                                /* First argument to xInput */
................................................................................
  pRet = (sqlite3_changeset_iter *)sqlite3_malloc(nByte);
  if( !pRet ) return SQLITE_NOMEM;
  memset(pRet, 0, sizeof(sqlite3_changeset_iter));
  pRet->in.aData = (u8 *)pChangeset;
  pRet->in.nData = nChangeset;
  pRet->in.xInput = xInput;
  pRet->in.pIn = pIn;
  pRet->in.iNext = 0;
  pRet->in.bEof = (xInput ? 0 : 1);

  /* Populate the output variable and return success. */
  *pp = pRet;
  return SQLITE_OK;
}

................................................................................
int sqlite3changeset_start_strm(
  sqlite3_changeset_iter **pp,    /* OUT: Changeset iterator handle */
  int (*xInput)(void *pIn, void *pData, int *pnData),
  void *pIn
){
  return sessionChangesetStart(pp, xInput, pIn, 0, 0);
}


















/*
** Ensure that there are at least nByte bytes available in the buffer. Or,
** if there are not nByte bytes remaining in the input, that all available
** data is in the buffer.
**
** Return an SQLite error code if an error occurs, or SQLITE_OK otherwise.
................................................................................
*/
static int sessionInputBuffer(SessionInput *pIn, int nByte){
  int rc = SQLITE_OK;
  if( pIn->xInput ){
    while( !pIn->bEof && (pIn->iNext+nByte)>=pIn->nData && rc==SQLITE_OK ){
      int nNew = SESSIONS_STRM_CHUNK_SIZE;

      if( pIn->iNext>=SESSIONS_STRM_CHUNK_SIZE ){
        int nMove = pIn->buf.nBuf - pIn->iNext;
        memmove(pIn->buf.aBuf, &pIn->buf.aBuf[pIn->iNext], nMove);
        pIn->buf.nBuf -= pIn->iNext;
        pIn->iNext = 0;
      }

      if( SQLITE_OK==sessionBufferGrow(&pIn->buf, nNew, &rc) ){
        rc = pIn->xInput(pIn->pIn, &pIn->buf.aBuf[pIn->buf.nBuf], &nNew);
        if( nNew==0 ){
          pIn->bEof = 1;
        }else{
          pIn->buf.nBuf += nNew;
        }
................................................................................
  if( p->rc!=SQLITE_OK ) return p->rc;

  /* If the iterator is already at the end of the changeset, return DONE. */
  if( p->in.iNext>=p->in.nData ){
    return SQLITE_DONE;
  }




  op = p->in.aData[p->in.iNext++];
  if( op=='T' || op=='P' ){
    p->bPatchset = (op=='P');
    if( sessionChangesetReadTblhdr(p) ) return p->rc;
    if( (p->rc = sessionInputBuffer(&p->in, 2)) ) return p->rc;

    op = p->in.aData[p->in.iNext++];
  }

  p->op = op;
  p->bIndirect = p->in.aData[p->in.iNext++];
  if( p->op!=SQLITE_UPDATE && p->op!=SQLITE_DELETE && p->op!=SQLITE_INSERT ){
    return (p->rc = SQLITE_CORRUPT_BKPT);
................................................................................
  sqlite3_stmt *pDelete;          /* DELETE statement */
  sqlite3_stmt *pUpdate;          /* UPDATE statement */
  sqlite3_stmt *pInsert;          /* INSERT statement */
  sqlite3_stmt *pSelect;          /* SELECT statement */
  int nCol;                       /* Size of azCol[] and abPK[] arrays */
  const char **azCol;             /* Array of column names */
  u8 *abPK;                       /* Boolean array - true if column is in PK */



};

/*
** Formulate a statement to DELETE a row from database db. Assuming a table
** structure like this:
**
**     CREATE TABLE x(a, b, c, d, PRIMARY KEY(a, c));
................................................................................
}

/*
** Iterator pIter must point to an SQLITE_INSERT entry. This function 
** transfers new.* values from the current iterator entry to statement
** pStmt. The table being inserted into has nCol columns.
**
** New.* value $i 0 from the iterator is bound to variable ($i+1) of 
** statement pStmt. If parameter abPK is NULL, all values from 0 to (nCol-1)
** are transfered to the statement. Otherwise, if abPK is not NULL, it points
** to an array nCol elements in size. In this case only those values for 
** which abPK[$i] is true are read from the iterator and bound to the 
** statement.
**
** An SQLite error code is returned if an error occurs. Otherwise, SQLITE_OK.
................................................................................
  if( rc==SQLITE_ROW ){
    /* There exists another row with the new.* primary key. */
    pIter->pConflict = p->pSelect;
    res = xConflict(pCtx, eType, pIter);
    pIter->pConflict = 0;
    rc = sqlite3_reset(p->pSelect);
  }else if( rc==SQLITE_OK ){








    /* No other row with the new.* primary key. */
    res = xConflict(pCtx, eType+1, pIter);
    if( res==SQLITE_CHANGESET_REPLACE ) rc = SQLITE_MISUSE;

  }

  if( rc==SQLITE_OK ){
    switch( res ){
      case SQLITE_CHANGESET_REPLACE:
        assert( pbReplace );
        *pbReplace = 1;
................................................................................
          SQLITE_CHANGESET_CONFLICT, p, pIter, xConflict, pCtx, pbReplace
      );
    }
  }

  return rc;
}



























































































/*
** Argument pIter is a changeset iterator that has been initialized, but
** not yet passed to sqlite3changeset_next(). This function applies the 
** changeset to the main database attached to handle "db". The supplied
** conflict handler callback is invoked to resolve any conflicts encountered
** while applying the change.
................................................................................
  int rc;                         /* Return code */
  const char *zTab = 0;           /* Name of current table */
  int nTab = 0;                   /* Result of sqlite3Strlen30(zTab) */
  SessionApplyCtx sApply;         /* changeset_apply() context object */

  assert( xConflict!=0 );


  memset(&sApply, 0, sizeof(sApply));
  sqlite3_mutex_enter(sqlite3_db_mutex(db));
  rc = sqlite3_exec(db, "SAVEPOINT changeset_apply", 0, 0, 0);
  if( rc==SQLITE_OK ){
    rc = sqlite3_exec(db, "PRAGMA defer_foreign_keys = 1", 0, 0, 0);
  }
  while( rc==SQLITE_OK && SQLITE_ROW==sqlite3changeset_next(pIter) ){
    int nCol;
    int op;
    int bReplace = 0;
    int bRetry = 0;
    const char *zNew;
    
    sqlite3changeset_op(pIter, &zNew, &nCol, &op, 0);

    if( zTab==0 || sqlite3_strnicmp(zNew, zTab, nTab+1) ){
      u8 *abPK;






      sqlite3_free((char*)sApply.azCol);  /* cast works around VC++ bug */
      sqlite3_finalize(sApply.pDelete);
      sqlite3_finalize(sApply.pUpdate); 
      sqlite3_finalize(sApply.pInsert);
      sqlite3_finalize(sApply.pSelect);
      memset(&sApply, 0, sizeof(sApply));
      sApply.db = db;


      /* If an xFilter() callback was specified, invoke it now. If the 
      ** xFilter callback returns zero, skip this table. If it returns
      ** non-zero, proceed. */
      schemaMismatch = (xFilter && (0==xFilter(pCtx, zNew)));
      if( schemaMismatch ){
        zTab = sqlite3_mprintf("%s", zNew);
................................................................................
      }
    }

    /* If there is a schema mismatch on the current table, proceed to the
    ** next change. A log message has already been issued. */
    if( schemaMismatch ) continue;

    rc = sessionApplyOneOp(pIter, &sApply, xConflict, pCtx, &bReplace, &bRetry);

    if( rc==SQLITE_OK && bRetry ){
      rc = sessionApplyOneOp(pIter, &sApply, xConflict, pCtx, &bReplace, 0);
    }

    if( bReplace ){
      assert( pIter->op==SQLITE_INSERT );
      rc = sqlite3_exec(db, "SAVEPOINT replace_op", 0, 0, 0);
      if( rc==SQLITE_OK ){
        rc = sessionBindRow(pIter, 
            sqlite3changeset_new, sApply.nCol, sApply.abPK, sApply.pDelete);
        sqlite3_bind_int(sApply.pDelete, sApply.nCol+1, 1);
      }
      if( rc==SQLITE_OK ){
        sqlite3_step(sApply.pDelete);
        rc = sqlite3_reset(sApply.pDelete);
      }
      if( rc==SQLITE_OK ){
        rc = sessionApplyOneOp(pIter, &sApply, xConflict, pCtx, 0, 0);
      }
      if( rc==SQLITE_OK ){
        rc = sqlite3_exec(db, "RELEASE replace_op", 0, 0, 0);
      }
    }

  }

  if( rc==SQLITE_OK ){
    rc = sqlite3changeset_finalize(pIter);
  }else{
    sqlite3changeset_finalize(pIter);
  }
................................................................................
  }

  sqlite3_finalize(sApply.pInsert);
  sqlite3_finalize(sApply.pDelete);
  sqlite3_finalize(sApply.pUpdate);
  sqlite3_finalize(sApply.pSelect);
  sqlite3_free((char*)sApply.azCol);  /* cast works around VC++ bug */

  sqlite3_mutex_leave(sqlite3_db_mutex(db));
  return rc;
}

/*
** Apply the changeset passed via pChangeset/nChangeset to the main database
** attached to handle "db". Invoke the supplied conflict handler callback







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/*
** An object of this type is used internally as an abstraction for 
** input data. Input data may be supplied either as a single large buffer
** (e.g. sqlite3changeset_start()) or using a stream function (e.g.
**  sqlite3changeset_start_strm()).
*/
struct SessionInput {
  int bNoDiscard;                 /* If true, discard no data */
  int iCurrent;                   /* Offset in aData[] of current change */
  int iNext;                      /* Offset in aData[] of next change */
  u8 *aData;                      /* Pointer to buffer containing changeset */
  int nData;                      /* Number of bytes in aData */

  SessionBuffer buf;              /* Current read buffer */
  int (*xInput)(void*, void*, int*);        /* Input stream call (or NULL) */
  void *pIn;                                /* First argument to xInput */
................................................................................
  pRet = (sqlite3_changeset_iter *)sqlite3_malloc(nByte);
  if( !pRet ) return SQLITE_NOMEM;
  memset(pRet, 0, sizeof(sqlite3_changeset_iter));
  pRet->in.aData = (u8 *)pChangeset;
  pRet->in.nData = nChangeset;
  pRet->in.xInput = xInput;
  pRet->in.pIn = pIn;

  pRet->in.bEof = (xInput ? 0 : 1);

  /* Populate the output variable and return success. */
  *pp = pRet;
  return SQLITE_OK;
}

................................................................................
int sqlite3changeset_start_strm(
  sqlite3_changeset_iter **pp,    /* OUT: Changeset iterator handle */
  int (*xInput)(void *pIn, void *pData, int *pnData),
  void *pIn
){
  return sessionChangesetStart(pp, xInput, pIn, 0, 0);
}

/*
** If the SessionInput object passed as the only argument is a streaming
** object and the buffer is full, discard some data to free up space.
*/
static void sessionDiscardData(SessionInput *pIn){
  if( pIn->bEof && pIn->xInput && pIn->iNext>=SESSIONS_STRM_CHUNK_SIZE ){
    int nMove = pIn->buf.nBuf - pIn->iNext;
    assert( nMove>=0 );
    if( nMove>0 ){
      memmove(pIn->buf.aBuf, &pIn->buf.aBuf[pIn->iNext], nMove);
    }
    pIn->buf.nBuf -= pIn->iNext;
    pIn->iNext = 0;
    pIn->nData = pIn->buf.nBuf;
  }
}

/*
** Ensure that there are at least nByte bytes available in the buffer. Or,
** if there are not nByte bytes remaining in the input, that all available
** data is in the buffer.
**
** Return an SQLite error code if an error occurs, or SQLITE_OK otherwise.
................................................................................
*/
static int sessionInputBuffer(SessionInput *pIn, int nByte){
  int rc = SQLITE_OK;
  if( pIn->xInput ){
    while( !pIn->bEof && (pIn->iNext+nByte)>=pIn->nData && rc==SQLITE_OK ){
      int nNew = SESSIONS_STRM_CHUNK_SIZE;

      if( pIn->bNoDiscard==0 ) sessionDiscardData(pIn);






      if( SQLITE_OK==sessionBufferGrow(&pIn->buf, nNew, &rc) ){
        rc = pIn->xInput(pIn->pIn, &pIn->buf.aBuf[pIn->buf.nBuf], &nNew);
        if( nNew==0 ){
          pIn->bEof = 1;
        }else{
          pIn->buf.nBuf += nNew;
        }
................................................................................
  if( p->rc!=SQLITE_OK ) return p->rc;

  /* If the iterator is already at the end of the changeset, return DONE. */
  if( p->in.iNext>=p->in.nData ){
    return SQLITE_DONE;
  }

  sessionDiscardData(&p->in);
  p->in.iCurrent = p->in.iNext;

  op = p->in.aData[p->in.iNext++];
  if( op=='T' || op=='P' ){
    p->bPatchset = (op=='P');
    if( sessionChangesetReadTblhdr(p) ) return p->rc;
    if( (p->rc = sessionInputBuffer(&p->in, 2)) ) return p->rc;
    p->in.iCurrent = p->in.iNext;
    op = p->in.aData[p->in.iNext++];
  }

  p->op = op;
  p->bIndirect = p->in.aData[p->in.iNext++];
  if( p->op!=SQLITE_UPDATE && p->op!=SQLITE_DELETE && p->op!=SQLITE_INSERT ){
    return (p->rc = SQLITE_CORRUPT_BKPT);
................................................................................
  sqlite3_stmt *pDelete;          /* DELETE statement */
  sqlite3_stmt *pUpdate;          /* UPDATE statement */
  sqlite3_stmt *pInsert;          /* INSERT statement */
  sqlite3_stmt *pSelect;          /* SELECT statement */
  int nCol;                       /* Size of azCol[] and abPK[] arrays */
  const char **azCol;             /* Array of column names */
  u8 *abPK;                       /* Boolean array - true if column is in PK */

  int bDeferConstraints;          /* True to defer constraints */
  SessionBuffer constraints;      /* Deferred constraints are stored here */
};

/*
** Formulate a statement to DELETE a row from database db. Assuming a table
** structure like this:
**
**     CREATE TABLE x(a, b, c, d, PRIMARY KEY(a, c));
................................................................................
}

/*
** Iterator pIter must point to an SQLITE_INSERT entry. This function 
** transfers new.* values from the current iterator entry to statement
** pStmt. The table being inserted into has nCol columns.
**
** New.* value $i from the iterator is bound to variable ($i+1) of 
** statement pStmt. If parameter abPK is NULL, all values from 0 to (nCol-1)
** are transfered to the statement. Otherwise, if abPK is not NULL, it points
** to an array nCol elements in size. In this case only those values for 
** which abPK[$i] is true are read from the iterator and bound to the 
** statement.
**
** An SQLite error code is returned if an error occurs. Otherwise, SQLITE_OK.
................................................................................
  if( rc==SQLITE_ROW ){
    /* There exists another row with the new.* primary key. */
    pIter->pConflict = p->pSelect;
    res = xConflict(pCtx, eType, pIter);
    pIter->pConflict = 0;
    rc = sqlite3_reset(p->pSelect);
  }else if( rc==SQLITE_OK ){
    if( p->bDeferConstraints && eType==SQLITE_CHANGESET_CONFLICT ){
      /* Instead of invoking the conflict handler, append the change blob
      ** to the SessionApplyCtx.constraints buffer. */
      u8 *aBlob = &pIter->in.aData[pIter->in.iCurrent];
      int nBlob = pIter->in.iNext - pIter->in.iCurrent;
      sessionAppendBlob(&p->constraints, aBlob, nBlob, &rc);
      res = SQLITE_CHANGESET_OMIT;
    }else{
      /* No other row with the new.* primary key. */
      res = xConflict(pCtx, eType+1, pIter);
      if( res==SQLITE_CHANGESET_REPLACE ) rc = SQLITE_MISUSE;
    }
  }

  if( rc==SQLITE_OK ){
    switch( res ){
      case SQLITE_CHANGESET_REPLACE:
        assert( pbReplace );
        *pbReplace = 1;
................................................................................
          SQLITE_CHANGESET_CONFLICT, p, pIter, xConflict, pCtx, pbReplace
      );
    }
  }

  return rc;
}

static int sessionApplyOneWithRetry(
  sqlite3 *db,                    /* Apply change to "main" db of this handle */
  sqlite3_changeset_iter *pIter,  /* Changeset iterator to read change from */
  SessionApplyCtx *pApply,        /* Apply context */
  int(*xConflict)(void*, int, sqlite3_changeset_iter*),
  void *pCtx                      /* First argument passed to xConflict */
){
  int bReplace = 0;
  int bRetry = 0;
  int rc;

  rc = sessionApplyOneOp(pIter, pApply, xConflict, pCtx, &bReplace, &bRetry);

  if( rc==SQLITE_OK && bRetry ){
    rc = sessionApplyOneOp(pIter, pApply, xConflict, pCtx, &bReplace, 0);
  }

  if( bReplace ){
    assert( pIter->op==SQLITE_INSERT );
    rc = sqlite3_exec(db, "SAVEPOINT replace_op", 0, 0, 0);
    if( rc==SQLITE_OK ){
      rc = sessionBindRow(pIter, 
          sqlite3changeset_new, pApply->nCol, pApply->abPK, pApply->pDelete);
      sqlite3_bind_int(pApply->pDelete, pApply->nCol+1, 1);
    }
    if( rc==SQLITE_OK ){
      sqlite3_step(pApply->pDelete);
      rc = sqlite3_reset(pApply->pDelete);
    }
    if( rc==SQLITE_OK ){
      rc = sessionApplyOneOp(pIter, pApply, xConflict, pCtx, 0, 0);
    }
    if( rc==SQLITE_OK ){
      rc = sqlite3_exec(db, "RELEASE replace_op", 0, 0, 0);
    }
  }

  return rc;
}

/*
** Retry the changes accumulated in the pApply->constraints buffer.
*/
static int sessionRetryConstraints(
  sqlite3 *db, 
  int bPatchset,
  const char *zTab,
  SessionApplyCtx *pApply,
  int(*xConflict)(void*, int, sqlite3_changeset_iter*),
  void *pCtx                      /* First argument passed to xConflict */
){
  int rc = SQLITE_OK;

  while( pApply->constraints.nBuf ){
    sqlite3_changeset_iter *pIter2 = 0;
    SessionBuffer cons = pApply->constraints;
    memset(&pApply->constraints, 0, sizeof(SessionBuffer));

    rc = sessionChangesetStart(&pIter2, 0, 0, cons.nBuf, cons.aBuf);
    if( rc==SQLITE_OK ){
      int nByte = 2*pApply->nCol*sizeof(sqlite3_value*);
      int rc2;
      pIter2->bPatchset = bPatchset;
      pIter2->zTab = (char*)zTab;
      pIter2->nCol = pApply->nCol;
      pIter2->abPK = pApply->abPK;
      sessionBufferGrow(&pIter2->tblhdr, nByte, &rc);
      pIter2->apValue = (sqlite3_value**)pIter2->tblhdr.aBuf;
      if( rc==SQLITE_OK ) memset(pIter2->apValue, 0, nByte);

      while( rc==SQLITE_OK && SQLITE_ROW==sqlite3changeset_next(pIter2) ){
        rc = sessionApplyOneWithRetry(db, pIter2, pApply, xConflict, pCtx);
      }

      rc2 = sqlite3changeset_finalize(pIter2);
      if( rc==SQLITE_OK ) rc==rc2;
    }
    assert( pApply->bDeferConstraints || pApply->constraints.nBuf==0 );

    sqlite3_free(cons.aBuf);
    if( rc!=SQLITE_OK ) break;
    if( pApply->constraints.nBuf>=cons.nBuf ){
      /* No progress was made on the last round. */
      pApply->bDeferConstraints = 0;
    }
  }

  return rc;
}

/*
** Argument pIter is a changeset iterator that has been initialized, but
** not yet passed to sqlite3changeset_next(). This function applies the 
** changeset to the main database attached to handle "db". The supplied
** conflict handler callback is invoked to resolve any conflicts encountered
** while applying the change.
................................................................................
  int rc;                         /* Return code */
  const char *zTab = 0;           /* Name of current table */
  int nTab = 0;                   /* Result of sqlite3Strlen30(zTab) */
  SessionApplyCtx sApply;         /* changeset_apply() context object */

  assert( xConflict!=0 );

  pIter->in.bNoDiscard = 1;
  memset(&sApply, 0, sizeof(sApply));
  sqlite3_mutex_enter(sqlite3_db_mutex(db));
  rc = sqlite3_exec(db, "SAVEPOINT changeset_apply", 0, 0, 0);
  if( rc==SQLITE_OK ){
    rc = sqlite3_exec(db, "PRAGMA defer_foreign_keys = 1", 0, 0, 0);
  }
  while( rc==SQLITE_OK && SQLITE_ROW==sqlite3changeset_next(pIter) ){
    int nCol;
    int op;


    const char *zNew;
    
    sqlite3changeset_op(pIter, &zNew, &nCol, &op, 0);

    if( zTab==0 || sqlite3_strnicmp(zNew, zTab, nTab+1) ){
      u8 *abPK;

      rc = sessionRetryConstraints(
          db, pIter->bPatchset, zTab, &sApply, xConflict, pCtx
      );
      if( rc!=SQLITE_OK ) break;

      sqlite3_free((char*)sApply.azCol);  /* cast works around VC++ bug */
      sqlite3_finalize(sApply.pDelete);
      sqlite3_finalize(sApply.pUpdate); 
      sqlite3_finalize(sApply.pInsert);
      sqlite3_finalize(sApply.pSelect);
      memset(&sApply, 0, sizeof(sApply));
      sApply.db = db;
      sApply.bDeferConstraints = 1;

      /* If an xFilter() callback was specified, invoke it now. If the 
      ** xFilter callback returns zero, skip this table. If it returns
      ** non-zero, proceed. */
      schemaMismatch = (xFilter && (0==xFilter(pCtx, zNew)));
      if( schemaMismatch ){
        zTab = sqlite3_mprintf("%s", zNew);
................................................................................
      }
    }

    /* If there is a schema mismatch on the current table, proceed to the
    ** next change. A log message has already been issued. */
    if( schemaMismatch ) continue;




    rc = sessionApplyOneWithRetry(db, pIter, &sApply, xConflict, pCtx);
  }




  if( rc==SQLITE_OK ){
    rc = sessionRetryConstraints(








        db, pIter->bPatchset, zTab, &sApply, xConflict, pCtx





    );
  }

  if( rc==SQLITE_OK ){
    rc = sqlite3changeset_finalize(pIter);
  }else{
    sqlite3changeset_finalize(pIter);
  }
................................................................................
  }

  sqlite3_finalize(sApply.pInsert);
  sqlite3_finalize(sApply.pDelete);
  sqlite3_finalize(sApply.pUpdate);
  sqlite3_finalize(sApply.pSelect);
  sqlite3_free((char*)sApply.azCol);  /* cast works around VC++ bug */
  sqlite3_free((char*)sApply.constraints.aBuf);
  sqlite3_mutex_leave(sqlite3_db_mutex(db));
  return rc;
}

/*
** Apply the changeset passed via pChangeset/nChangeset to the main database
** attached to handle "db". Invoke the supplied conflict handler callback