SQLite

static void fts5DebugRowid(int *pRc, Fts5Buffer *pBuf, i64 iKey){
  int iSegid, iHeight, iPgno, bDlidx;       /* Rowid compenents */
  fts5DecodeRowid(iKey, &iSegid, &bDlidx, &iHeight, &iPgno);

  if( iSegid==0 ){
    if( iKey==FTS5_AVERAGES_ROWID ){
      sqlite3Fts5BufferAppendPrintf(pRc, pBuf, "{averages} ");
    }else{
      sqlite3Fts5BufferAppendPrintf(pRc, pBuf, "{structure}");
    }
  }
  else{
    sqlite3Fts5BufferAppendPrintf(pRc, pBuf, "{%ssegid=%d h=%d pgno=%d}",
        bDlidx ? "dlidx " : "", iSegid, iHeight, iPgno
    );
  }
}

static void fts5DebugStructure(
  int *pRc,                       /* IN/OUT: error code */

}
do_execsql_test 2.1 {
  INSERT INTO t1 VALUES('a b c', 'd e f');
}

do_test 2.2 {
  execsql { SELECT fts5_decode(id, block) FROM t1_data WHERE id==10 }
} {/{{structure} {lvl=0 nMerge=0 nSeg=1 {id=[0123456789]* h=0 leaves=1..1}}}/}

foreach w {a b c d e f} {
  do_execsql_test 2.3.$w.asc {
    SELECT rowid FROM t1 WHERE t1 MATCH $w;
  } {1}
  do_execsql_test 2.3.$w.desc {
    SELECT rowid FROM t1 WHERE t1 MATCH $w ORDER BY rowid DESC;

  2 { SELECT rowid FROM t1 WHERE t1 MATCH 'x + w'   }  [list $W]
  3 { SELECT rowid FROM t1 WHERE t1 MATCH 'x AND w' }  [list $W]
  4 { SELECT rowid FROM t1 WHERE t1 MATCH 'y AND x' }  [list $Y]
" {

  do_test 1.6.$tn.1 {
    set n [execsql_reads $q]
    #puts -nonewline "(n=$n nReadX=$nReadX)"
    expr {$n < ($nReadX / 8)}
  } {1}

  do_test 1.6.$tn.2 {
    set n [execsql_reads "$q ORDER BY rowid DESC"]
    #puts -nonewline "(n=$n nReadX=$nReadX)"
    expr {$n < ($nReadX / 8)}
  } {1}

  do_execsql_test 1.6.$tn.3 $q [lsort -int -incr $res]
  do_execsql_test 1.6.$tn.4 "$q ORDER BY rowid DESC" [lsort -int -decr $res]
}

#-------------------------------------------------------------------------
# Process command line arguments.
#
proc usage {} {
  puts stderr "usage: $::argv0 ?OPTIONS? database table"
  puts stderr ""
  puts stderr "  -nterm                (count number of terms in each segment)"
  puts stderr ""
  exit 1
}

set O(nterm) 0

if {[llength $argv]<2} usage
foreach a [lrange $argv 0 end-2] {
  switch -- $a {
    -nterm {
      set O(nterm) 1
    }

    default {
      usage
    }
  }
}

set database [lindex $argv end-1]
set tbl [lindex $argv end]


#-------------------------------------------------------------------------
# Count the number of terms in each segment of fts5 table $tbl. Store the
# counts in the array variable in the parent context named by parameter
# $arrayname, indexed by segment-id. Example:
#
#   count_terms fts_tbl A
#   foreach {k v} [array get A] { puts "segid=$k nTerm=$v" }
#
proc count_terms {tbl arrayname} {
  upvar A $arrayname
  array unset A
  db eval "SELECT fts5_decode(rowid, block) AS d FROM ${tbl}_data" {
    set desc [lindex $d 0]
    if {[regexp {^segid=([0-9]*)} $desc -> id]} {
      foreach i [lrange $d 1 end] {
        if {[string match {term=*} $i]} { incr A($id) }
      }
    }
  }
}


#-------------------------------------------------------------------------
# Start of main program.
#
sqlite3 db $database
catch { load_static_extension db fts5 }

if {$O(nterm)} { count_terms $tbl A }

db eval "SELECT fts5_decode(rowid, block) AS d FROM ${tbl}_data WHERE id=10" {
  foreach lvl [lrange $d 1 end] {
    puts [lrange $lvl 0 2]

    foreach seg [lrange $lvl 3 end] {
      if {$::O(nterm)} {
        regexp {^id=([0-9]*)} $seg -> id
        set nTerm 0
        catch { set nTerm $A($id) }
        puts [format "        % -28s    nTerm=%d" $seg $nTerm]
      } else {
        puts [format "        % -28s" $seg]
      }
    }
  }
}