Yes, for those pgroll migrations that require a new column + backfill, starting the migration can be expensive.
Backfills are done in fixed size batches to avoid long lived row locks, but the operation can still be expensive in terms of time and potentially I/O. Options to control the rate of backfilling could be a useful addition here but they aren't present yet.
Backfills are done in fixed size batches to avoid long lived row locks, but the operation can still be expensive in terms of time and potentially I/O. Options to control the rate of backfilling could be a useful addition here but they aren't present yet.