[t:3008], add comments to leafentry struct describing format

git-svn-id: file:///svn/toku/tokudb@25153 c7de825b-a66e-492c-adef-691d508d4ae1

newbrt/leafentry.h

@@ -60,10 +60,27 @@ struct __attribute__ ((__packed__)) leafentry {
             uint32_t num_cxrs; // number of committed uxrs
             uint8_t  num_pxrs; // number of provisional uxrs
             u_int8_t key_xrs[0]; //Actual key,
-                                 //then interesting TXNIDs
-                                 //then interesting lengths (type bit is MSB of length)
-                                 //then interesting data
-                                 //then other transaction records
+                                 //then "interesting" TXNIDs:
+                                 //  if provisional uxrs exist, store OUTERMOST TXNID
+                                 //  then store committed TXNIDs, from most recently committed to least recently committed
+                                 //then "interesting" lengths (length is at most 1<<31, MSB is used to store the type bit):
+                                 //  if provisional uxrs exist, store length and type of INNERMOST TXNID
+                                 //  then store length and type of committed TXNIDs, in same order as above
+                                 //then "interesting" data
+                                 //  if provisional uxrs exist, store data for INNERMOST TXNID
+                                 //  then store data for committed TXNIDs
+                                 //if provisional uxrs still exist (that is, num_puxrs > 1, so INNERMOST provisional != OUTERMOST provisional):
+                                 //  for OUTERMOST provisional TXNID:
+                                 //    1 byte: store type
+                                 //    4 bytes: length (if type is INSERT)
+                                 //    data
+                                 //  for rest of provisional stack, from outermost to innermost, but NOT including innermost:
+                                 //   8 bytes: TXNID
+                                 //   1 byte: store type
+                                 //   4 bytes: length (if type is INSERT)
+                                 //   data
+                                 //  for INNERMOST provisional TXNID:
+                                 //   8 bytes: TXNID
         } mvcc; // For the case where LEAFENTRY->type is LE_MVCC
     } u;
 };