Issue #14: post-review fixes: spelling, better comments and variable names

Test Plan: N/A

Reviewers: maykov, hermanlee4, yoshinorim, jonahcohen

Reviewed By: jonahcohen

Differential Revision: https://reviews.facebook.net/D33453

Author: spetrunia

storage/rocksdb/ha_rocksdb.cc

@@ -1676,8 +1676,8 @@ void ha_rocksdb::convert_record_to_storage_format(rocksdb::Slice *packed_rec)
 
   for (uint i=0; i < table->s->fields; i++)
   {
-    /* Don't pack decode-able PK key parts */
-    if (field_enc[i].skip)
+    /* Don't pack decodable PK key parts */
+    if (field_enc[i].dont_store)
       continue;
 
     Field *field= table->field[i];
@@ -1782,7 +1782,7 @@ int ha_rocksdb::convert_record_from_storage_format(uchar * buf)
 
   for (uint i=0; i < table->s->fields; i++)
   {
-    if (field_enc[i].skip)
+    if (field_enc[i].dont_store)
       continue;
 
     Field *field= table->field[i];
@@ -1882,6 +1882,10 @@ int ha_rocksdb::convert_record_from_storage_format(uchar * buf)
 
 /*
   Setup data needed to convert table->record[] to and from record storage format.
+
+  @seealso
+     ha_rocksdb::convert_record_to_storage_format,
+     ha_rocksdb::convert_record_from_storage_format
 */
 
 void ha_rocksdb::setup_field_converters()
@@ -1896,7 +1900,7 @@ void ha_rocksdb::setup_field_converters()
   for (i= 0; i < table->s->fields; i++)
   {
     Field *field= table->field[i];
-    field_enc[i].skip= false;
+    field_enc[i].dont_store= false;
 
     /*
       Check if this field is
@@ -1910,10 +1914,11 @@ void ha_rocksdb::setup_field_converters()
       KEY *pk_info= &table->key_info[table->s->primary_key];
       for (uint kp= 0; kp < pk_info->user_defined_key_parts; kp++)
       {
+        /* key_part->fieldnr is counted from 1 */
         if (field->field_index + 1 == pk_info->key_part[kp].fieldnr)
         {
           if (pk_descr->can_unpack(kp))
-            field_enc[i].skip= true; /* Don't store */
+            field_enc[i].dont_store= true;
           break;
         }
       }

storage/rocksdb/ha_rocksdb.h

@@ -197,8 +197,13 @@ class ha_rocksdb: public handler
   */
   typedef struct st_field_encoder
   {
-    /* skip=true means this is decodeable part of PK and so not stored */
-    bool skip;
+    /*
+      This is set to true for columns of Primary Key that can be decoded from
+      their mem-comparable form.
+      Since we can get them from the key part of RocksDB key->value pair, we
+      don't need to store them in the value part.
+    */
+    bool dont_store;
 
     uint null_offset;
     uchar null_mask;  // 0 means the field cannot be null

storage/rocksdb/rdb_datadic.h

@@ -50,7 +50,15 @@ class Stream_reader
     if (len)
       ptr= &str.at(0);
     else
+    {
+      /*
+        One can a create a Stream_reader for reading from an empty string
+        (although attempts to read anything will fail).
+        We must not access str.at(0), since len==0, we can set ptr to any
+        value.
+      */
       ptr= NULL;
+    }
   }
 
   explicit Stream_reader(const rocksdb::Slice *slice)