Index: ext/fts3/fts3.c
==================================================================
--- ext/fts3/fts3.c
+++ ext/fts3/fts3.c
@@ -1903,22 +1903,25 @@
 typedef enum fulltext_statement {
   CONTENT_INSERT_STMT,
   CONTENT_SELECT_STMT,
   CONTENT_UPDATE_STMT,
   CONTENT_DELETE_STMT,
+  CONTENT_EXISTS_STMT,
 
   BLOCK_INSERT_STMT,
   BLOCK_SELECT_STMT,
   BLOCK_DELETE_STMT,
+  BLOCK_DELETE_ALL_STMT,
 
   SEGDIR_MAX_INDEX_STMT,
   SEGDIR_SET_STMT,
   SEGDIR_SELECT_LEVEL_STMT,
   SEGDIR_SPAN_STMT,
   SEGDIR_DELETE_STMT,
   SEGDIR_SELECT_SEGMENT_STMT,
   SEGDIR_SELECT_ALL_STMT,
+  SEGDIR_DELETE_ALL_STMT,
 
   MAX_STMT                     /* Always at end! */
 } fulltext_statement;
 
 /* These must exactly match the enum above. */
@@ -1929,15 +1932,17 @@
 static const char *const fulltext_zStatement[MAX_STMT] = {
   /* CONTENT_INSERT */ NULL,  /* generated in contentInsertStatement() */
   /* CONTENT_SELECT */ NULL,  /* generated in contentSelectStatement() */
   /* CONTENT_UPDATE */ NULL,  /* generated in contentUpdateStatement() */
   /* CONTENT_DELETE */ "delete from %_content where docid = ?",
+  /* CONTENT_EXISTS */ "select docid from %_content limit 1",
 
   /* BLOCK_INSERT */
   "insert into %_segments (blockid, block) values (null, ?)",
   /* BLOCK_SELECT */ "select block from %_segments where blockid = ?",
   /* BLOCK_DELETE */ "delete from %_segments where blockid between ? and ?",
+  /* BLOCK_DELETE_ALL */ "delete from %_segments",
 
   /* SEGDIR_MAX_INDEX */ "select max(idx) from %_segdir where level = ?",
   /* SEGDIR_SET */ "insert into %_segdir values (?, ?, ?, ?, ?, ?)",
   /* SEGDIR_SELECT_LEVEL */
   "select start_block, leaves_end_block, root from %_segdir "
@@ -1954,11 +1959,11 @@
   "select start_block, leaves_end_block, root from %_segdir "
   " where level = ? and idx = ?",
   /* SEGDIR_SELECT_ALL */
   "select start_block, leaves_end_block, root from %_segdir "
   " order by level desc, idx asc",
-
+  /* SEGDIR_DELETE_ALL */ "delete from %_segdir",
 };
 
 /*
 ** A connection to a fulltext index is an instance of the following
 ** structure.  The xCreate and xConnect methods create an instance
@@ -2247,10 +2252,29 @@
   rc = sqlite3_bind_int64(s, 1, iDocid);
   if( rc!=SQLITE_OK ) return rc;
 
   return sql_single_step(s);
 }
+
+/* Returns SQLITE_ROW if any rows exist in %_content, SQLITE_DONE if
+** no rows exist, and any error in case of failure.
+*/
+static int content_exists(fulltext_vtab *v){
+  sqlite3_stmt *s;
+  int rc = sql_get_statement(v, CONTENT_EXISTS_STMT, &s);
+  if( rc!=SQLITE_OK ) return rc;
+
+  rc = sqlite3_step(s);
+  if( rc!=SQLITE_ROW ) return rc;
+
+  /* We expect only one row.  We must execute another sqlite3_step()
+   * to complete the iteration; otherwise the table will remain locked. */
+  rc = sqlite3_step(s);
+  if( rc==SQLITE_DONE ) return SQLITE_ROW;
+  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
+  return rc;
+}
 
 /* insert into %_segments values ([pData])
 **   returns assigned blockid in *piBlockid
 */
 static int block_insert(fulltext_vtab *v, const char *pData, int nData,
@@ -2419,10 +2443,27 @@
   if( rc!=SQLITE_OK ) return rc;
 
   rc = sqlite3_bind_int64(s, 1, iLevel);
   if( rc!=SQLITE_OK ) return rc;
 
+  return sql_single_step(s);
+}
+
+/* Delete entire fts index, SQLITE_OK on success, relevant error on
+** failure.
+*/
+static int segdir_delete_all(fulltext_vtab *v){
+  sqlite3_stmt *s;
+  int rc = sql_get_statement(v, SEGDIR_DELETE_ALL_STMT, &s);
+  if( rc!=SQLITE_OK ) return rc;
+
+  rc = sql_single_step(s);
+  if( rc!=SQLITE_OK ) return rc;
+
+  rc = sql_get_statement(v, BLOCK_DELETE_ALL_STMT, &s);
+  if( rc!=SQLITE_OK ) return rc;
+
   return sql_single_step(s);
 }
 
 /* TODO(shess) clearPendingTerms() is far down the file because
 ** writeZeroSegment() is far down the file because LeafWriter is far
@@ -6110,10 +6151,27 @@
 
   FTSTRACE(("FTS3 Update %p\n", pVtab));
 
   if( nArg<2 ){
     rc = index_delete(v, sqlite3_value_int64(ppArg[0]));
+    if( rc==SQLITE_OK ){
+      /* If we just deleted the last row in the table, clear out the
+      ** index data.
+      */
+      rc = content_exists(v);
+      if( rc==SQLITE_ROW ){
+        rc = SQLITE_OK;
+      }else if( rc==SQLITE_DONE ){
+        /* Clear the pending terms so we don't flush a useless level-0
+        ** segment when the transaction closes.
+        */
+        rc = clearPendingTerms(v);
+        if( rc==SQLITE_OK ){
+          rc = segdir_delete_all(v);
+        }
+      }
+    }
   } else if( sqlite3_value_type(ppArg[0]) != SQLITE_NULL ){
     /* An update:
      * ppArg[0] = old rowid
      * ppArg[1] = new rowid
      * ppArg[2..2+v->nColumn-1] = values

ADDED   test/fts3d.test
Index: test/fts3d.test
==================================================================
--- test/fts3d.test
+++ test/fts3d.test
@@ -0,0 +1,128 @@
+# 2008 June 26
+#
+# 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 SQLite library.  The focus
+# of this script is testing the FTS3 module's optimize() function.
+#
+# $Id: fts3d.test,v 1.1 2008/07/14 20:43:15 shess Exp $
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+
+# If SQLITE_ENABLE_FTS3 is not defined, omit this file.
+ifcapable !fts3 {
+  finish_test
+  return
+}
+
+#*************************************************************************
+# Probe to see if support for the FTS3 dump_* functions is compiled in.
+# TODO(shess): Change main.mk to do the right thing and remove this test.
+db eval {
+  DROP TABLE IF EXISTS t1;
+  CREATE VIRTUAL TABLE t1 USING fts3(c);
+  INSERT INTO t1 (docid, c) VALUES (1, 'x');
+}
+
+set s {SELECT dump_terms(t1, 1) FROM t1 LIMIT 1}
+set r {1 {unable to use function dump_terms in the requested context}}
+if {[catchsql $s]==$r} {
+  finish_test
+  return
+}
+
+#*************************************************************************
+# Utility function to check for the expected terms in the segment
+# level/index.  _all version does same but for entire index.
+proc check_terms {test level index terms} {
+  # TODO(shess): Figure out why uplevel in do_test can't catch
+  # $level and $index directly.
+  set ::level $level
+  set ::index $index
+  do_test $test.terms {
+    execsql {
+      SELECT dump_terms(t1, $::level, $::index) FROM t1 LIMIT 1;
+    }
+  } [list $terms]
+}
+proc check_terms_all {test terms} {
+  do_test $test.terms {
+    execsql {
+      SELECT dump_terms(t1) FROM t1 LIMIT 1;
+    }
+  } [list $terms]
+}
+
+# Utility function to check for the expected doclist for the term in
+# segment level/index.  _all version does same for entire index.
+proc check_doclist {test level index term doclist} {
+  # TODO(shess): Again, why can't the non-:: versions work?
+  set ::term $term
+  set ::level $level
+  set ::index $index
+  do_test $test {
+    execsql {
+      SELECT dump_doclist(t1, $::term, $::level, $::index) FROM t1 LIMIT 1;
+    }
+  } [list $doclist]
+}
+proc check_doclist_all {test term doclist} {
+  set ::term $term
+  do_test $test {
+    execsql {
+      SELECT dump_doclist(t1, $::term) FROM t1 LIMIT 1;
+    }
+  } [list $doclist]
+}
+
+#*************************************************************************
+# Test results when all rows are deleted and one is added back.
+# Previously older segments would continue to exist, but now the index
+# should be dropped when the table is empty.  The results should look
+# exactly like we never added the earlier rows in the first place.
+db eval {
+  DROP TABLE IF EXISTS t1;
+  CREATE VIRTUAL TABLE t1 USING fts3(c);
+  INSERT INTO t1 (docid, c) VALUES (1, 'This is a test');
+  INSERT INTO t1 (docid, c) VALUES (2, 'That was a test');
+  INSERT INTO t1 (docid, c) VALUES (3, 'This is a test');
+  DELETE FROM t1 WHERE 1=1; -- Delete each row rather than dropping table.
+  INSERT INTO t1 (docid, c) VALUES (1, 'This is a test');
+}
+
+# Should be a single initial segment.
+do_test fts3d-1.segments {
+  execsql {
+    SELECT level, idx FROM t1_segdir ORDER BY level, idx;
+  }
+} {0 0}
+do_test fts3d-1.matches {
+  execsql {
+    SELECT OFFSETS(t1) FROM t1
+     WHERE t1 MATCH 'this OR that OR was OR a OR is OR test' ORDER BY docid;
+  }
+} {{0 0 0 4 0 4 5 2 0 3 8 1 0 5 10 4}}
+
+check_terms_all fts3d-1.1 {a is test this}
+check_doclist_all fts3d-1.1.1 a {[1 0[2]]}
+check_doclist_all fts3d-1.1.2 is {[1 0[1]]}
+check_doclist_all fts3d-1.1.3 test {[1 0[3]]}
+check_doclist_all fts3d-1.1.4 this {[1 0[0]]}
+
+check_terms   fts3d-1.2   0 0 {a is test this}
+check_doclist fts3d-1.2.1 0 0 a {[1 0[2]]}
+check_doclist fts3d-1.2.2 0 0 is {[1 0[1]]}
+check_doclist fts3d-1.2.3 0 0 test {[1 0[3]]}
+check_doclist fts3d-1.2.4 0 0 this {[1 0[0]]}
+
+# TODO(shess): optimize() tests here.
+
+finish_test