Correctly handle indexes on column prefixes

Summary:
The code used table->field[n] when packing/unpacking index values.
This happens to work most of the time, however the right way to
do it is to use table->key_info[i].key_part[j], which has a field
object that describes the field use in the index.

Differential Revision: https://reviews.facebook.net/D39471

storage/rocksdb/ha_rocksdb.cc

@@ -2735,7 +2735,7 @@ bool ha_rocksdb::check_keyread_allowed(uint inx, uint part, bool all_parts) cons
   KEY *key_info= &table_share->key_info[inx];
 
   Field_pack_info dummy1;
-  res= dummy1.setup(key_info->key_part[part].field);
+  res= dummy1.setup(key_info->key_part[part].field, inx, part);
 
   if (res && all_parts)
   {
@@ -2745,7 +2745,7 @@ bool ha_rocksdb::check_keyread_allowed(uint inx, uint part, bool all_parts) cons
       if ((field= key_info->key_part[i].field))
       {
         Field_pack_info dummy;
-        if (!dummy.setup(field))
+        if (!dummy.setup(field, inx, i))
         {
           /* Cannot do index-only reads for this column */
           res= false;

storage/rocksdb/rdb_datadic.cc

@@ -204,8 +204,11 @@ void RDBSE_KEYDEF::setup(TABLE *tbl)
     int max_part_len= 0;
     bool simulating_extkey= false;
     uint dst_i= 0;
+
+    uint keyno_to_set= keyno;
+    uint keypart_to_set= 0;
     /* this loop also loops over the 'extended key' tail */
-    for (uint src_i= 0; src_i < m_key_parts; src_i++)
+    for (uint src_i= 0; src_i < m_key_parts; src_i++, keypart_to_set++)
     {
       Field *field= key_part->field;
 
@@ -232,7 +235,7 @@ void RDBSE_KEYDEF::setup(TABLE *tbl)
       if (field->real_maybe_null())
         max_len +=1; // NULL-byte
 
-      pack_info[dst_i].setup(field);
+      pack_info[dst_i].setup(field, keyno_to_set, keypart_to_set);
       pack_info[dst_i].unpack_data_offset= unpack_len;
 
       if (pk_info)
@@ -258,6 +261,8 @@ void RDBSE_KEYDEF::setup(TABLE *tbl)
       if (secondary_key && src_i+1 == key_info->actual_key_parts)
       {
         simulating_extkey= true;
+        keyno_to_set= tbl->s->primary_key;
+        keypart_to_set= (uint)-1;
         key_part= pk_info->key_part;
       }
 
@@ -343,8 +348,9 @@ uint RDBSE_KEYDEF::get_primary_key_tuple(TABLE *table,
 
     if (have_value)
     {
-      Field *field= table->field[pack_info[i].fieldnr];
-      if (pack_info[i].skip_func(&pack_info[i], field, &reader))
+      Field_pack_info *fpi= &pack_info[i];
+      Field *field= fpi->get_field_in_table(table);
+      if (fpi->skip_func(fpi, field, &reader))
         return INVALID_LEN;
     }
 
@@ -460,7 +466,7 @@ uint RDBSE_KEYDEF::pack_record(TABLE *tbl,
 
   for (uint i=0; i < n_key_parts; i++)
   {
-    Field *field= tbl->field[pack_info[i].fieldnr];
+    Field *field= pack_info[i].get_field_in_table(tbl);
 
     // Old Field methods expected the record pointer to be at tbl->record[0].
     // The quick and easy way to fix this was to pass along the offset
@@ -629,7 +635,7 @@ int RDBSE_KEYDEF::unpack_record(TABLE *table, uchar *buf,
   for (uint i= 0; i < m_key_parts ; i++)
   {
     Field_pack_info *fpi= &pack_info[i];
-    Field *field= table->field[pack_info[i].fieldnr];
+    Field *field= fpi->get_field_in_table(table);
 
     if (fpi->unpack_func)
     {
@@ -1016,12 +1022,14 @@ int skip_variable_length(Field_pack_info *fpi, Field *field, Stream_reader *read
     FALSE -  Otherwise
 */
 
-bool Field_pack_info::setup(Field *field)
+bool Field_pack_info::setup(Field *field, uint keynr_arg, uint key_part_arg)
 {
   int res= false;
   enum_field_types type= field->real_type();
 
-  fieldnr= field->field_index;
+  keynr= keynr_arg;
+  key_part= key_part_arg;
+
   maybe_null= field->real_maybe_null();
   make_unpack_info_func= NULL;
   unpack_func= NULL;
@@ -1107,6 +1115,11 @@ bool Field_pack_info::setup(Field *field)
 }
 
 
+Field *Field_pack_info::get_field_in_table(TABLE *tbl)
+{
+  return tbl->key_info[keynr].key_part[key_part].field;
+}
+
 #if 0
 void _rdbse_store_blob_length(uchar *pos,uint pack_length,uint length)
 {

storage/rocksdb/rdb_datadic.h

@@ -440,10 +440,34 @@ class Field_pack_info
   */
   index_field_skip_t skip_func;
 
-  /* Number of field in the table */
-  int fieldnr;
-
-  bool setup(Field *field);
+private:
+  /*
+    Location of the field in the table (key number and key part number).
+
+    Note that this describes not the field, but rather a position of field in
+    the index. Consider an example:
+
+      col1 VARCHAR (100),
+      INDEX idx1 (col1)),
+      INDEX idx2 (col1(10)),
+
+    Here, idx2 has a special Field object that is set to describe a 10-char
+    prefix of col1.
+
+    We must also store the keynr. It is needed for implicit "extended keys".
+    Every key in MyRocks needs to include PK columns.  Generally, SQL layer
+    includes PK columns as part of its "Extended Keys" feature, but sometimes
+    it does not (known examples are unique secondary indexes and partitioned
+    tables).
+    In that case, MyRocks's index descriptor has invisible suffix of PK
+    columns (and the point is that these columns are parts of PK, not parts
+    of the current index).
+  */
+  uint keynr;
+  uint key_part;
+public:
+  bool setup(Field *field, uint keynr_arg, uint key_part_arg);
+  Field *get_field_in_table(TABLE *tbl);
 };