refs #5179 improve comment for get_next_ule that fixed hot indexing but, and...

refs #5179 improve comment for get_next_ule that fixed hot indexing but, and document the client contract regarding hot db writes and index create/abort/close


git-svn-id: file:///svn/toku/tokudb@45190 c7de825b-a66e-492c-adef-691d508d4ae1

src/indexer.c

@@ -410,7 +410,8 @@ build_index(DB_INDEXER *indexer) {
         // grab the next leaf entry and get its provisional info. we'll
         // need the provisional info for the undo-do algorithm, and we get
         // it here so it can be read atomically with respect to txn commit
-        // and abort.
+        // and abort. the atomicity comes from the root-to-leaf path pinned
+        // by the query and in the getf callback function
         //
         // this allocates space for the prov info, so we have to destroy it
         // when we're done.
@@ -471,6 +472,7 @@ build_index(DB_INDEXER *indexer) {
     return result;
 }
 
+// Clients must not operate on any of the hot dbs concurrently with close
 static int 
 close_indexer(DB_INDEXER *indexer) {
     int r = 0;
@@ -498,6 +500,7 @@ close_indexer(DB_INDEXER *indexer) {
     return r;
 }
 
+// Clients must not operate on any of the hot dbs concurrently with abort
 static int 
 abort_indexer(DB_INDEXER *indexer) {
     (void) __sync_fetch_and_sub(&STATUS_VALUE(INDEXER_CURRENT), 1);

src/indexer.h

@@ -43,6 +43,8 @@ void toku_indexer_unlock(DB_INDEXER* indexer);
 //
 // Returns 0 if the indexer has been created and sets *indexer to the indexer object.
 // If an error occurred while creating the indexer object, a non-zero error number is returned.
+//
+// Clients must not operate on any of the dest_dbs concurrently with create_indexer();
 int toku_indexer_create_indexer(DB_ENV *env,
                                 DB_TXN *txn,
                                 DB_INDEXER **indexer,