Insert at most 1,000 rows at once in MR diff background migration

We were hitting the statement timeout for very large MR diffs. Now we insert at
most 1,000 rows to `merge_request_diff_commits` in a single statement, or 100
rows to `merge_request_diff_files`.

1 files changed, 9 insertions, 3 deletions

diff --git a/lib/gitlab/background_migration/deserialize_merge_request_diffs_and_commits.rb b/lib/gitlab/background_migration/deserialize_merge_request_diffs_and_commits.rb
index 3fde1b09efb..6f1fd0a333d 100644
--- a/lib/gitlab/background_migration/deserialize_merge_request_diffs_and_commits.rb
+++ b/lib/gitlab/background_migration/deserialize_merge_request_diffs_and_commits.rb
@@ -8,6 +8,7 @@ module Gitlab
       end
 
       BUFFER_ROWS = 1000
+      DIFF_FILE_BUFFER_ROWS = 100
 
       def perform(start_id, stop_id)
         merge_request_diffs = MergeRequestDiff
@@ -26,7 +27,7 @@ module Gitlab
 
           if diff_ids.length > BUFFER_ROWS ||
               commit_rows.length > BUFFER_ROWS ||
-              file_rows.length > BUFFER_ROWS
+              file_rows.length > DIFF_FILE_BUFFER_ROWS
 
             flush_buffers!
           end
@@ -46,8 +47,13 @@ module Gitlab
       def flush_buffers!
         if diff_ids.any?
           MergeRequestDiff.transaction do
-            Gitlab::Database.bulk_insert('merge_request_diff_commits', commit_rows)
-            Gitlab::Database.bulk_insert('merge_request_diff_files', file_rows)
+            commit_rows.each_slice(BUFFER_ROWS).each do |commit_rows_slice|
+              Gitlab::Database.bulk_insert('merge_request_diff_commits', commit_rows_slice)
+            end
+
+            file_rows.each_slice(DIFF_FILE_BUFFER_ROWS).each do |file_rows_slice|
+              Gitlab::Database.bulk_insert('merge_request_diff_files', file_rows_slice)
+            end
 
             MergeRequestDiff.where(id: diff_ids).update_all(st_commits: nil, st_diffs: nil)
           end