[GitHub] [incubator-doris] wutiangan commented on a change in pull request #3993: Keep order of read from segment consist with the write order

[GitBox <gi...@apache.org>]

wutiangan commented on a change in pull request #3993:
URL: https://github.com/apache/incubator-doris/pull/3993#discussion_r448288786



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File path: be/src/olap/generic_iterators.cpp
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@@ -227,8 +229,13 @@ class MergeIterator : public RowwiseIterator {
         bool operator()(const MergeIteratorContext* lhs, const MergeIteratorContext* rhs) const {
             auto lhs_row = lhs->current_row();
             auto rhs_row = rhs->current_row();
-
-            return compare_row(lhs_row, rhs_row) > 0;
+            int cmp_res = compare_row(lhs_row, rhs_row);
+            if (cmp_res !=  0) {
+                return cmp_res > 0;
+            }
+            // if row cursors equal, compare segment id.

Review comment:
       add some comments why  sort by row asc, and sort by segment_id desc.




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