branch-4.0: [opt](memory) set source content column by column when flush memtable for partial update (#59547)

pick #58782

### What problem does this PR solve?

related issue: #58780

Under the load to 5000-columns wide table, flush memtable consume lots
of memory:
<img width="526" height="430" alt="image"

src="https://github.com/user-attachments/assets/816bcc8b-d9d0-4105-a96b-3fbcc931b0b1"
/>

Set source content column by column when flush memtable for partial
update to solve this problem, the memory usage of
`_append_block_with_partial_content` is hardly visible in the profile
after optimization.

### What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

### Release note

None

### Check List (For Author)

- Test <!-- At least one of them must be included. -->
    - [ ] Regression test
    - [ ] Unit Test
    - [ ] Manual test (add detailed scripts or steps below)
    - [ ] No need to test or manual test. Explain why:
- [ ] This is a refactor/code format and no logic has been changed.
        - [ ] Previous test can cover this change.
        - [ ] No code files have been changed.
        - [ ] Other reason <!-- Add your reason?  -->

- Behavior changed:
    - [ ] No.
    - [ ] Yes. <!-- Explain the behavior change -->

- Does this need documentation?
    - [ ] No.
- [ ] Yes. <!-- Add document PR link here. eg:
apache/doris-website#1214 -->

### Check List (For Reviewer who merge this PR)

- [ ] Confirm the release note
- [ ] Confirm test cases
- [ ] Confirm document
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Author: sollhui

be/src/olap/rowset/segment_v2/vertical_segment_writer.cpp

@@ -528,15 +528,15 @@ Status VerticalSegmentWriter::_append_block_with_partial_content(RowsInBlock& da
     for (auto i : including_cids) {
         full_block.replace_by_position(i, data.block->get_by_position(input_id++).column);
     }
-    RETURN_IF_ERROR(_olap_data_convertor->set_source_content_with_specifid_columns(
-            &full_block, data.row_pos, data.num_rows, including_cids));
 
     bool have_input_seq_column = false;
     // write including columns
     std::vector<vectorized::IOlapColumnDataAccessor*> key_columns;
     vectorized::IOlapColumnDataAccessor* seq_column = nullptr;
     uint32_t segment_start_pos = 0;
     for (auto cid : including_cids) {
+        RETURN_IF_ERROR(_olap_data_convertor->set_source_content_with_specifid_columns(
+                &full_block, data.row_pos, data.num_rows, std::vector<uint32_t> {cid}));
         // here we get segment column row num before append data.
         segment_start_pos = cast_set<uint32_t>(_column_writers[cid]->get_next_rowid());
         // olap data convertor alway start from id = 0
@@ -554,6 +554,15 @@ Status VerticalSegmentWriter::_append_block_with_partial_content(RowsInBlock& da
         RETURN_IF_ERROR(_column_writers[cid]->append(column->get_nullmap(), column->get_data(),
                                                      data.num_rows));
         RETURN_IF_ERROR(_finalize_column_writer_and_update_meta(cid));
+        // Don't clear source content for key columns and sequence column here,
+        // as they will be used later in _full_encode_keys() and _generate_primary_key_index().
+        // They will be cleared at the end of this method.
+        bool is_key_column = (cid < _num_sort_key_columns);
+        bool is_seq_column = (_tablet_schema->has_sequence_col() &&
+                              cid == _tablet_schema->sequence_col_idx() && have_input_seq_column);
+        if (!is_key_column && !is_seq_column) {
+            _olap_data_convertor->clear_source_content(cid);
+        }
     }
 
     bool has_default_or_nullable = false;
@@ -629,9 +638,9 @@ Status VerticalSegmentWriter::_append_block_with_partial_content(RowsInBlock& da
 
     // convert missing columns and send to column writer
     const auto& missing_cids = _opts.rowset_ctx->partial_update_info->missing_cids;
-    RETURN_IF_ERROR(_olap_data_convertor->set_source_content_with_specifid_columns(
-            &full_block, data.row_pos, data.num_rows, missing_cids));
     for (auto cid : missing_cids) {
+        RETURN_IF_ERROR(_olap_data_convertor->set_source_content_with_specifid_columns(
+                &full_block, data.row_pos, data.num_rows, std::vector<uint32_t> {cid}));
         auto [status, column] = _olap_data_convertor->convert_column_data(cid);
         if (!status.ok()) {
             return status;
@@ -644,6 +653,13 @@ Status VerticalSegmentWriter::_append_block_with_partial_content(RowsInBlock& da
         RETURN_IF_ERROR(_column_writers[cid]->append(column->get_nullmap(), column->get_data(),
                                                      data.num_rows));
         RETURN_IF_ERROR(_finalize_column_writer_and_update_meta(cid));
+        // Don't clear source content for sequence column here if it will be used later
+        // in _generate_primary_key_index(). It will be cleared at the end of this method.
+        bool is_seq_column = (_tablet_schema->has_sequence_col() && !have_input_seq_column &&
+                              cid == _tablet_schema->sequence_col_idx());
+        if (!is_seq_column) {
+            _olap_data_convertor->clear_source_content(cid);
+        }
     }
 
     _num_rows_updated += stats.num_rows_updated;