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Overview
Comment:Add the ability to disable the covering-index-scan optimization at compile-time, start-time, or at run-time. Add test cases to check this configurability.
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SHA1: ccb8ecc30c8e6c7760131250297c2e452bbac43b
User & Date: drh 2012-09-17 20:44:46
Context
2012-09-17
21:24
Make sure the WHERE_IDX_ONLY flag is not set on query plans that will not be using an index. Closed-Leaf check-in: 698b2a28 user: drh tags: fullscan-covering-index
20:44
Add the ability to disable the covering-index-scan optimization at compile-time, start-time, or at run-time. Add test cases to check this configurability. check-in: ccb8ecc3 user: drh tags: fullscan-covering-index
19:26
Merge recent trunk changes into the fullscan-covering-index branch. check-in: 1c0bf030 user: drh tags: fullscan-covering-index
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/global.c.

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};
#endif

#ifndef SQLITE_USE_URI
# define  SQLITE_USE_URI 0
#endif





/*
** The following singleton contains the global configuration for
** the SQLite library.
*/
SQLITE_WSD struct Sqlite3Config sqlite3Config = {
   SQLITE_DEFAULT_MEMSTATUS,  /* bMemstat */
   1,                         /* bCoreMutex */
   SQLITE_THREADSAFE==1,      /* bFullMutex */
   SQLITE_USE_URI,            /* bOpenUri */

   0x7ffffffe,                /* mxStrlen */
   128,                       /* szLookaside */
   500,                       /* nLookaside */
   {0,0,0,0,0,0,0,0},         /* m */
   {0,0,0,0,0,0,0,0,0},       /* mutex */
   {0,0,0,0,0,0,0,0,0,0,0,0,0},/* pcache2 */
   (void*)0,                  /* pHeap */







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};
#endif

#ifndef SQLITE_USE_URI
# define  SQLITE_USE_URI 0
#endif

#ifndef SQLITE_ALLOW_COVERING_INDEX_SCAN
# define SQLITE_ALLOW_COVERING_INDEX_SCAN 1
#endif

/*
** The following singleton contains the global configuration for
** the SQLite library.
*/
SQLITE_WSD struct Sqlite3Config sqlite3Config = {
   SQLITE_DEFAULT_MEMSTATUS,  /* bMemstat */
   1,                         /* bCoreMutex */
   SQLITE_THREADSAFE==1,      /* bFullMutex */
   SQLITE_USE_URI,            /* bOpenUri */
   SQLITE_ALLOW_COVERING_INDEX_SCAN,   /* bUseCis */
   0x7ffffffe,                /* mxStrlen */
   128,                       /* szLookaside */
   500,                       /* nLookaside */
   {0,0,0,0,0,0,0,0},         /* m */
   {0,0,0,0,0,0,0,0,0},       /* mutex */
   {0,0,0,0,0,0,0,0,0,0,0,0,0},/* pcache2 */
   (void*)0,                  /* pHeap */

Changes to src/main.c.

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      break;
    }

    case SQLITE_CONFIG_URI: {
      sqlite3GlobalConfig.bOpenUri = va_arg(ap, int);
      break;
    }






    default: {
      rc = SQLITE_ERROR;
      break;
    }
  }
  va_end(ap);







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      break;
    }

    case SQLITE_CONFIG_URI: {
      sqlite3GlobalConfig.bOpenUri = va_arg(ap, int);
      break;
    }

    case SQLITE_CONFIG_COVERING_INDEX_SCAN: {
      sqlite3GlobalConfig.bUseCis = va_arg(ap, int);
      break;
    }

    default: {
      rc = SQLITE_ERROR;
      break;
    }
  }
  va_end(ap);

Changes to src/sqlite.h.in.

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** specified as part of [ATTACH] commands are interpreted as URIs, regardless
** of whether or not the [SQLITE_OPEN_URI] flag is set when the database
** connection is opened. If it is globally disabled, filenames are
** only interpreted as URIs if the SQLITE_OPEN_URI flag is set when the
** database connection is opened. By default, URI handling is globally
** disabled. The default value may be changed by compiling with the
** [SQLITE_USE_URI] symbol defined.












**
** [[SQLITE_CONFIG_PCACHE]] [[SQLITE_CONFIG_GETPCACHE]]
** <dt>SQLITE_CONFIG_PCACHE and SQLITE_CONFIG_GETPCACHE
** <dd> These options are obsolete and should not be used by new code.
** They are retained for backwards compatibility but are now no-ops.
** </dl>
*/
................................................................................
#define SQLITE_CONFIG_LOOKASIDE    13  /* int int */
#define SQLITE_CONFIG_PCACHE       14  /* no-op */
#define SQLITE_CONFIG_GETPCACHE    15  /* no-op */
#define SQLITE_CONFIG_LOG          16  /* xFunc, void* */
#define SQLITE_CONFIG_URI          17  /* int */
#define SQLITE_CONFIG_PCACHE2      18  /* sqlite3_pcache_methods2* */
#define SQLITE_CONFIG_GETPCACHE2   19  /* sqlite3_pcache_methods2* */


/*
** CAPI3REF: Database Connection Configuration Options
**
** These constants are the available integer configuration options that
** can be passed as the second argument to the [sqlite3_db_config()] interface.
**







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** specified as part of [ATTACH] commands are interpreted as URIs, regardless
** of whether or not the [SQLITE_OPEN_URI] flag is set when the database
** connection is opened. If it is globally disabled, filenames are
** only interpreted as URIs if the SQLITE_OPEN_URI flag is set when the
** database connection is opened. By default, URI handling is globally
** disabled. The default value may be changed by compiling with the
** [SQLITE_USE_URI] symbol defined.
**
** [[SQLITE_CONFIG_COVERING_INDEX_SCAN]] <dt>SQLITE_CONFIG_COVERING_INDEX_SCAN
** <dd> This option taks a single integer argument which is interpreted as
** a boolean in order to enable or disable the use of covering indices for
** full table scans in the query optimizer.  The default setting is determined
** by the [SQLITE_ALLOW_COVERING_INDEX_SCAN] compile-time option, or is "on"
** if that compile-time option is omitted.
** The ability to disable the use of covering indices for full table scans
** is because some incorrectly coded legacy applications might malfunction
** malfunction when the optimization is enabled.  Providing the ability to
** disable the optimization allows the older, buggy application code to work
** without change even with newer versions of SQLite.
**
** [[SQLITE_CONFIG_PCACHE]] [[SQLITE_CONFIG_GETPCACHE]]
** <dt>SQLITE_CONFIG_PCACHE and SQLITE_CONFIG_GETPCACHE
** <dd> These options are obsolete and should not be used by new code.
** They are retained for backwards compatibility but are now no-ops.
** </dl>
*/
................................................................................
#define SQLITE_CONFIG_LOOKASIDE    13  /* int int */
#define SQLITE_CONFIG_PCACHE       14  /* no-op */
#define SQLITE_CONFIG_GETPCACHE    15  /* no-op */
#define SQLITE_CONFIG_LOG          16  /* xFunc, void* */
#define SQLITE_CONFIG_URI          17  /* int */
#define SQLITE_CONFIG_PCACHE2      18  /* sqlite3_pcache_methods2* */
#define SQLITE_CONFIG_GETPCACHE2   19  /* sqlite3_pcache_methods2* */
#define SQLITE_CONFIG_COVERING_INDEX_SCAN 20  /* int */

/*
** CAPI3REF: Database Connection Configuration Options
**
** These constants are the available integer configuration options that
** can be passed as the second argument to the [sqlite3_db_config()] interface.
**

Changes to src/sqliteInt.h.

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*/
#define SQLITE_QueryFlattener 0x01   /* Disable query flattening */
#define SQLITE_ColumnCache    0x02   /* Disable the column cache */
#define SQLITE_GroupByOrder   0x04   /* Disable GROUPBY cover of ORDERBY */
#define SQLITE_FactorOutConst 0x08   /* Disable factoring out constants */
#define SQLITE_IdxRealAsInt   0x10   /* Store REAL as INT in indices */
#define SQLITE_DistinctOpt    0x20   /* DISTINCT using indexes */

#define SQLITE_OptMask        0xff   /* Mask of all disablable opts */

/*
** Possible values for the sqlite.magic field.
** The numbers are obtained at random and have no special meaning, other
** than being distinct from one another.
*/
................................................................................
** This structure also contains some state information.
*/
struct Sqlite3Config {
  int bMemstat;                     /* True to enable memory status */
  int bCoreMutex;                   /* True to enable core mutexing */
  int bFullMutex;                   /* True to enable full mutexing */
  int bOpenUri;                     /* True to interpret filenames as URIs */

  int mxStrlen;                     /* Maximum string length */
  int szLookaside;                  /* Default lookaside buffer size */
  int nLookaside;                   /* Default lookaside buffer count */
  sqlite3_mem_methods m;            /* Low-level memory allocation interface */
  sqlite3_mutex_methods mutex;      /* Low-level mutex interface */
  sqlite3_pcache_methods2 pcache2;  /* Low-level page-cache interface */
  void *pHeap;                      /* Heap storage space */







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*/
#define SQLITE_QueryFlattener 0x01   /* Disable query flattening */
#define SQLITE_ColumnCache    0x02   /* Disable the column cache */
#define SQLITE_GroupByOrder   0x04   /* Disable GROUPBY cover of ORDERBY */
#define SQLITE_FactorOutConst 0x08   /* Disable factoring out constants */
#define SQLITE_IdxRealAsInt   0x10   /* Store REAL as INT in indices */
#define SQLITE_DistinctOpt    0x20   /* DISTINCT using indexes */
#define SQLITE_CoverIdxScan   0x40   /* Disable covering index scans */
#define SQLITE_OptMask        0xff   /* Mask of all disablable opts */

/*
** Possible values for the sqlite.magic field.
** The numbers are obtained at random and have no special meaning, other
** than being distinct from one another.
*/
................................................................................
** This structure also contains some state information.
*/
struct Sqlite3Config {
  int bMemstat;                     /* True to enable memory status */
  int bCoreMutex;                   /* True to enable core mutexing */
  int bFullMutex;                   /* True to enable full mutexing */
  int bOpenUri;                     /* True to interpret filenames as URIs */
  int bUseCis;                      /* Use covering indices for full-scans */
  int mxStrlen;                     /* Maximum string length */
  int szLookaside;                  /* Default lookaside buffer size */
  int nLookaside;                   /* Default lookaside buffer count */
  sqlite3_mem_methods m;            /* Low-level memory allocation interface */
  sqlite3_mutex_methods mutex;      /* Low-level mutex interface */
  sqlite3_pcache_methods2 pcache2;  /* Low-level page-cache interface */
  void *pHeap;                      /* Heap storage space */

Changes to src/test1.c.

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    { "all",              SQLITE_OptMask        },
    { "query-flattener",  SQLITE_QueryFlattener },
    { "column-cache",     SQLITE_ColumnCache    },
    { "groupby-order",    SQLITE_GroupByOrder   },
    { "factor-constants", SQLITE_FactorOutConst },
    { "real-as-int",      SQLITE_IdxRealAsInt   },
    { "distinct-opt",     SQLITE_DistinctOpt    },

  };

  if( objc!=4 ){
    Tcl_WrongNumArgs(interp, 1, objv, "DB OPT BOOLEAN");
    return TCL_ERROR;
  }
  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;







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    { "all",              SQLITE_OptMask        },
    { "query-flattener",  SQLITE_QueryFlattener },
    { "column-cache",     SQLITE_ColumnCache    },
    { "groupby-order",    SQLITE_GroupByOrder   },
    { "factor-constants", SQLITE_FactorOutConst },
    { "real-as-int",      SQLITE_IdxRealAsInt   },
    { "distinct-opt",     SQLITE_DistinctOpt    },
    { "cover-idx-scan",   SQLITE_CoverIdxScan   },
  };

  if( objc!=4 ){
    Tcl_WrongNumArgs(interp, 1, objv, "DB OPT BOOLEAN");
    return TCL_ERROR;
  }
  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;

Changes to src/test_malloc.c.

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  }

  rc = sqlite3_config(SQLITE_CONFIG_URI, bOpenUri);
  Tcl_SetResult(interp, (char *)sqlite3TestErrorName(rc), TCL_VOLATILE);

  return TCL_OK;
}






























/*
** Usage:    sqlite3_dump_memsys3  FILENAME
**           sqlite3_dump_memsys5  FILENAME
**
** Write a summary of unfreed memsys3 allocations to FILENAME.
*/
................................................................................
     { "sqlite3_db_status",          test_db_status                ,0 },
     { "install_malloc_faultsim",    test_install_malloc_faultsim  ,0 },
     { "sqlite3_config_heap",        test_config_heap              ,0 },
     { "sqlite3_config_memstatus",   test_config_memstatus         ,0 },
     { "sqlite3_config_lookaside",   test_config_lookaside         ,0 },
     { "sqlite3_config_error",       test_config_error             ,0 },
     { "sqlite3_config_uri",         test_config_uri               ,0 },

     { "sqlite3_db_config_lookaside",test_db_config_lookaside      ,0 },
     { "sqlite3_dump_memsys3",       test_dump_memsys3             ,3 },
     { "sqlite3_dump_memsys5",       test_dump_memsys3             ,5 },
     { "sqlite3_install_memsys3",    test_install_memsys3          ,0 },
     { "sqlite3_memdebug_vfs_oom_test", test_vfs_oom_test          ,0 },
  };
  int i;







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  }

  rc = sqlite3_config(SQLITE_CONFIG_URI, bOpenUri);
  Tcl_SetResult(interp, (char *)sqlite3TestErrorName(rc), TCL_VOLATILE);

  return TCL_OK;
}

/*
** Usage:    sqlite3_config_cis  BOOLEAN
**
** Enables or disables the use of the covering-index scan optimization.
** SQLITE_CONFIG_COVERING_INDEX_SCAN.
*/
static int test_config_cis(
  void * clientData, 
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  int rc;
  int bUseCis;

  if( objc!=2 ){
    Tcl_WrongNumArgs(interp, 1, objv, "BOOL");
    return TCL_ERROR;
  }
  if( Tcl_GetBooleanFromObj(interp, objv[1], &bUseCis) ){
    return TCL_ERROR;
  }

  rc = sqlite3_config(SQLITE_CONFIG_COVERING_INDEX_SCAN, bUseCis);
  Tcl_SetResult(interp, (char *)sqlite3TestErrorName(rc), TCL_VOLATILE);

  return TCL_OK;
}

/*
** Usage:    sqlite3_dump_memsys3  FILENAME
**           sqlite3_dump_memsys5  FILENAME
**
** Write a summary of unfreed memsys3 allocations to FILENAME.
*/
................................................................................
     { "sqlite3_db_status",          test_db_status                ,0 },
     { "install_malloc_faultsim",    test_install_malloc_faultsim  ,0 },
     { "sqlite3_config_heap",        test_config_heap              ,0 },
     { "sqlite3_config_memstatus",   test_config_memstatus         ,0 },
     { "sqlite3_config_lookaside",   test_config_lookaside         ,0 },
     { "sqlite3_config_error",       test_config_error             ,0 },
     { "sqlite3_config_uri",         test_config_uri               ,0 },
     { "sqlite3_config_cis",         test_config_cis               ,0 },
     { "sqlite3_db_config_lookaside",test_db_config_lookaside      ,0 },
     { "sqlite3_dump_memsys3",       test_dump_memsys3             ,3 },
     { "sqlite3_dump_memsys5",       test_dump_memsys3             ,5 },
     { "sqlite3_install_memsys3",    test_install_memsys3          ,0 },
     { "sqlite3_memdebug_vfs_oom_test", test_vfs_oom_test          ,0 },
  };
  int i;

Changes to src/where.c.

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    ** The ANALYZE command and the sqlite_stat1 and sqlite_stat3 tables do
    ** not give us data on the relative sizes of table and index records.
    ** So this computation assumes table records are about twice as big
    ** as index records
    */
    if( wsFlags==WHERE_IDX_ONLY
     && (pWC->wctrlFlags & WHERE_ONEPASS_DESIRED)==0




    ){
      /* This index is not useful for indexing, but it is a covering index.
      ** A full-scan of the index might be a little faster than a full-scan
      ** of the table, so give this case a cost slightly less than a table
      ** scan. */
      cost = aiRowEst[0]*3;
      wsFlags |= WHERE_COVER_SCAN|WHERE_COLUMN_RANGE;
    }else if( (wsFlags & WHERE_NOT_FULLSCAN)==0 ){
      /* The cost of a full table scan is a number of move operations equal
      ** to the number of rows in the table.
      **
      ** We add an additional 4x penalty to full table scans.  This causes
      ** the cost function to err on the side of choosing an index over







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    ** The ANALYZE command and the sqlite_stat1 and sqlite_stat3 tables do
    ** not give us data on the relative sizes of table and index records.
    ** So this computation assumes table records are about twice as big
    ** as index records
    */
    if( wsFlags==WHERE_IDX_ONLY
     && (pWC->wctrlFlags & WHERE_ONEPASS_DESIRED)==0
     && sqlite3GlobalConfig.bUseCis
#ifndef SQLITE_OMIT_BUILTIN_TEST
     && (pParse->db->flags & SQLITE_CoverIdxScan)==0
#endif
    ){
      /* This index is not useful for indexing, but it is a covering index.
      ** A full-scan of the index might be a little faster than a full-scan
      ** of the table, so give this case a cost slightly less than a table
      ** scan. */
      cost = aiRowEst[0]*3 + pProbe->nColumn;
      wsFlags |= WHERE_COVER_SCAN|WHERE_COLUMN_RANGE;
    }else if( (wsFlags & WHERE_NOT_FULLSCAN)==0 ){
      /* The cost of a full table scan is a number of move operations equal
      ** to the number of rows in the table.
      **
      ** We add an additional 4x penalty to full table scans.  This causes
      ** the cost function to err on the side of choosing an index over

Added test/coveridxscan.test.



























































































































































































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# 2012 September 17
#
# 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.
#
#***********************************************************************
#
# Tests for the optimization which attempts to use a covering index
# for a full-table scan (under the theory that the index will be smaller
# and require less I/O and hence will run faster.)
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl

set testprefix coveridxscan

do_test 1.1 {
  db eval {
    CREATE TABLE t1(a,b,c);
    INSERT INTO t1 VALUES(5,4,3), (4,8,2), (3,2,1);
    CREATE INDEX t1ab ON t1(a,b);
    CREATE INDEX t1b ON t1(b);
    SELECT a FROM t1;
  }
  # covering index used for the scan, hence values are increasing
} {3 4 5}

do_test 1.2 {
  db eval {
    SELECT a, c FROM t1;
  }
  # There is no covering index, hence the values are in rowid order
} {5 3 4 2 3 1}

do_test 1.3 {
  db eval {
    SELECT b FROM t1;
  }
  # Choice of two indices: use the one with fewest columns
} {2 4 8}

do_test 2.1 {
  optimization_control db cover-idx-scan 0
  db eval {SELECT a FROM t1}
  # With the optimization turned off, output in rowid order
} {5 4 3}
do_test 2.2 {
  db eval {SELECT a, c FROM t1}
} {5 3 4 2 3 1}
do_test 2.3 {
  db eval {SELECT b FROM t1}
} {4 8 2}

db close
sqlite3_shutdown
sqlite3_config_cis 0
sqlite3 db test.db

do_test 3.1 {
  db eval {SELECT a FROM t1}
  # With the optimization configured off, output in rowid order
} {5 4 3}
do_test 3.2 {
  db eval {SELECT a, c FROM t1}
} {5 3 4 2 3 1}
do_test 3.3 {
  db eval {SELECT b FROM t1}
} {4 8 2}

db close
sqlite3_shutdown
sqlite3_config_cis 1
sqlite3 db test.db

# The CIS optimization is enabled again.  Covering indices are once again
# used for all table scans.
do_test 4.1 {
  db eval {SELECT a FROM t1}
} {3 4 5}
do_test 4.2 {
  db eval {SELECT a, c FROM t1}
} {5 3 4 2 3 1}
do_test 4.3 {
  db eval {SELECT b FROM t1}
} {2 4 8}


finish_test

Changes to test/eqp.test.

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}

# EVIDENCE-OF: R-40701-42164 sqlite> EXPLAIN QUERY PLAN SELECT a FROM
# t1 UNION SELECT c FROM t2; 1|0|0|SCAN TABLE t1 (~1000000 rows)
# 2|0|0|SCAN TABLE t2 (~1000000 rows) 0|0|0|COMPOUND SUBQUERIES 1 AND 2
# USING TEMP B-TREE (UNION)
det 5.12 "SELECT a FROM t1 UNION SELECT c FROM t2" {
  1 0 0 {SCAN TABLE t1 USING COVERING INDEX i2 (~1000000 rows)}
  2 0 0 {SCAN TABLE t2 USING COVERING INDEX i4 (~1000000 rows)}
  0 0 0 {COMPOUND SUBQUERIES 1 AND 2 USING TEMP B-TREE (UNION)}
}

# EVIDENCE-OF: R-61538-24748 sqlite> EXPLAIN QUERY PLAN SELECT a FROM
# t1 EXCEPT SELECT d FROM t2 ORDER BY 1; 1|0|0|SCAN TABLE t1 USING
# COVERING INDEX i2 (~1000000 rows) 2|0|0|SCAN TABLE t2 (~1000000 rows)







|







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}

# EVIDENCE-OF: R-40701-42164 sqlite> EXPLAIN QUERY PLAN SELECT a FROM
# t1 UNION SELECT c FROM t2; 1|0|0|SCAN TABLE t1 (~1000000 rows)
# 2|0|0|SCAN TABLE t2 (~1000000 rows) 0|0|0|COMPOUND SUBQUERIES 1 AND 2
# USING TEMP B-TREE (UNION)
det 5.12 "SELECT a FROM t1 UNION SELECT c FROM t2" {
  1 0 0 {SCAN TABLE t1 USING COVERING INDEX i1 (~1000000 rows)}
  2 0 0 {SCAN TABLE t2 USING COVERING INDEX i4 (~1000000 rows)}
  0 0 0 {COMPOUND SUBQUERIES 1 AND 2 USING TEMP B-TREE (UNION)}
}

# EVIDENCE-OF: R-61538-24748 sqlite> EXPLAIN QUERY PLAN SELECT a FROM
# t1 EXCEPT SELECT d FROM t2 ORDER BY 1; 1|0|0|SCAN TABLE t1 USING
# COVERING INDEX i2 (~1000000 rows) 2|0|0|SCAN TABLE t2 (~1000000 rows)