diff options
Diffstat (limited to 'app/models/concerns/each_batch.rb')
| -rw-r--r-- | app/models/concerns/each_batch.rb | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/app/models/concerns/each_batch.rb b/app/models/concerns/each_batch.rb index 8cf0b8b154d..6314b46a7e3 100644 --- a/app/models/concerns/each_batch.rb +++ b/app/models/concerns/each_batch.rb @@ -39,7 +39,15 @@ module EachBatch # # of - The number of rows to retrieve per batch. # column - The column to use for ordering the batches. - def each_batch(of: 1000, column: primary_key) + # order_hint - An optional column to append to the `ORDER BY id` + # clause to help the query planner. PostgreSQL might perform badly + # with a LIMIT 1 because the planner is guessing that scanning the + # index in ID order will come across the desired row in less time + # it will take the planner than using another index. The + # order_hint does not affect the search results. For example, + # `ORDER BY id ASC, updated_at ASC` means the same thing as `ORDER + # BY id ASC`. + def each_batch(of: 1000, column: primary_key, order_hint: nil) unless column raise ArgumentError, 'the column: argument must be set to a column name to use for ordering rows' @@ -48,7 +56,9 @@ module EachBatch start = except(:select) .select(column) .reorder(column => :asc) - .take + + start = start.order(order_hint) if order_hint + start = start.take return unless start @@ -60,6 +70,9 @@ module EachBatch .select(column) .where(arel_table[column].gteq(start_id)) .reorder(column => :asc) + + stop = stop.order(order_hint) if order_hint + stop = stop .offset(of) .limit(1) .take |