Reverse and incremental index sorting optimizations

h2/src/docsrc/html/changelog.html

@@ -21,6 +21,8 @@ <h1>Change Log</h1>
 
 <h2>Next Version (unreleased)</h2>
 <ul>
+<li>Issue #701: An available index is never used for ordering, when the requested order is DESC
+</li>
 <li>Issue #4036: NULLS NOT DISTINCT constraint changed after column dropped
 </li>
 <li>Issue #4033: Wrong array produced when using ARRAY_AGG() on UNNEST(ARRAY[CAST(? AS INT)]) expression

h2/src/docsrc/html/performance.html

@@ -732,6 +732,17 @@ <h3>Special Optimizations</h3>
 </p><p>
 For queries of the form <code>SELECT * FROM TEST ORDER BY ID</code>, the query plan includes the line
 <code>/* index sorted */</code> to indicate there is no separate sorting required.
+<code>/* index sorted: 2 of 3 columns */</code> indicates that only some columns are sorted with an index.
+An additional sorting is still required, but queries with the FETCH (TOP, LIMIT) clause
+may still stop their execution earlier.
+An index on <code>(A ASC, B ASC)</code> columns can be used for <code>ORDER BY A</code>, <code>ORDER BY A DESC</code>,
+<code>ORDER BY A, B</code> or <code>ORDER BY A DESC, B DESC</code>.
+With <code>ORDER BY A, B DESC</code> this index can only be used for ordering on the column <code>A</code>.
+If columns are nullable, order of nulls is also important. Index on <code>(A ASC NULLS FIRST)</code> cannot be used for
+<code>ORDER BY A ASC NULLS LAST</code>, but can be used for <code>ORDER BY A ASC NULLS FIRST</code> or
+<code>ORDER BY A DESC NULLS LAST</code>.
+When neither <code>NULLS FIRST</code> nor <code>NULLS LAST</code> is specified, a default is used, this default
+is controlled by <a href="commands.html#set_default_null_ordering"><code>DEFAULT_NULL_ORDERING</code></a> setting.
 </p><p>
 For queries of the form <code>SELECT * FROM TEST GROUP BY ID ORDER BY ID</code>, the query plan includes the line
 <code>/* group sorted */</code> to indicate there is no separate sorting required.

h2/src/main/org/h2/bnf/context/DbContextRule.java

@@ -89,7 +89,8 @@ public boolean autoComplete(Sentence sentence) {
                         best = quotedName;
                         bestSchema = schema;
                     }
-                } else if (s.isEmpty() || StringUtils.startsWithIgnoringCase(name, query) ||  StringUtils.startsWithIgnoringCase(quotedName, query)) {
+                } else if (s.isEmpty() || StringUtils.startsWithIgnoringCase(name, query)
+                        || StringUtils.startsWithIgnoringCase(quotedName, query)) {
                     if (s.length() < name.length()) {
                         sentence.add(name, name.substring(s.length()), type);
                         sentence.add(schema.quotedName + ".",
@@ -116,12 +117,14 @@ public boolean autoComplete(Sentence sentence) {
                 String name = table.getName();
                 String quotedName = StringUtils.quoteIdentifier(name);
 
-                if (StringUtils.startsWithIgnoringCase(query, name) || StringUtils.startsWithIgnoringCase("\"" + query, quotedName)) {
+                if (StringUtils.startsWithIgnoringCase(query, name)
+                        || StringUtils.startsWithIgnoringCase("\"" + query, quotedName)) {
                     if (best == null || name.length() > best.length()) {
                         best = name;
                         bestTable = table;
                     }
-                } else if (s.isEmpty() || StringUtils.startsWithIgnoringCase(name, query) ||  StringUtils.startsWithIgnoringCase(quotedName, query)) {
+                } else if (s.isEmpty() || StringUtils.startsWithIgnoringCase(name, query)
+                        || StringUtils.startsWithIgnoringCase(quotedName, query)) {
                     if (s.length() < name.length()) {
                         sentence.add(table.getQuotedName(),
                                 table.getQuotedName().substring(s.length()),

h2/src/main/org/h2/command/CommandRemote.java

@@ -286,7 +286,8 @@ public BatchResult executeBatchUpdate(ArrayList<Value[]> batchParameters, Object
                         }
                         if (readGeneratedKeys) {
                             int columnCount = transfer.readInt();
-                            ResultRemote remoteGeneratedKeys = new ResultRemote(session, transfer, objectId, columnCount, Integer.MAX_VALUE);
+                            ResultRemote remoteGeneratedKeys = new ResultRemote(session, transfer, objectId,
+                                    columnCount, Integer.MAX_VALUE);
                             generatedKeys.add(remoteGeneratedKeys);
                             remoteGeneratedKeys.close();
                         }
@@ -310,7 +311,8 @@ public BatchResult executeBatchUpdate(ArrayList<Value[]> batchParameters, Object
                                 autoCommit = transfer.readBoolean();
                                 if (readGeneratedKeys) {
                                     int columnCount = transfer.readInt();
-                                    ResultRemote remoteGeneratedKeys = new ResultRemote(session, transfer, objectId, columnCount, Integer.MAX_VALUE);
+                                    ResultRemote remoteGeneratedKeys = new ResultRemote(session, transfer, objectId,
+                                            columnCount, Integer.MAX_VALUE);
                                     generatedKeys.add(remoteGeneratedKeys);
                                     remoteGeneratedKeys.close();
                                 }

h2/src/main/org/h2/command/ddl/Analyze.java

@@ -187,7 +187,7 @@ public static void analyzeTable(SessionLocal session, Table table, int sample, b
         if (columnCount == 0) {
             return;
         }
-        Cursor cursor = table.getScanIndex(session).find(session, null, null);
+        Cursor cursor = table.getScanIndex(session).find(session, null, null, false);
         if (cursor.next()) {
             SelectivityData[] array = new SelectivityData[columnCount];
             for (int i = 0; i < columnCount; i++) {

h2/src/main/org/h2/command/dml/ScriptCommand.java

@@ -474,7 +474,7 @@ private static <T extends DbObject> T[] sorted(Collection<T> collection, Class<T
     private int generateInsertValues(int count, Table table) throws IOException {
         PlanItem plan = table.getBestPlanItem(session, null, null, -1, null, null);
         Index index = plan.getIndex();
-        Cursor cursor = index.find(session, null, null);
+        Cursor cursor = index.find(session, null, null, false);
         Column[] columns = table.getColumns();
         boolean withGenerated = false, withGeneratedAlwaysAsIdentity = false;
         for (Column c : columns) {