diff options
| author | ChangBo Guo(gcb) <eric.guo@easystack.cn> | 2017-02-06 10:38:05 +0800 |
|---|---|---|
| committer | ChangBo Guo(gcb) <eric.guo@easystack.cn> | 2017-02-06 23:24:35 +0800 |
| commit | 9fb3c018fc16c8f5b781c119dd3c148ed7954db7 (patch) | |
| tree | 616a323a837e5d329883416b7f2e40517da28112 | |
| parent | fcc794f531777ed1b80962ad700a166bff8c47c6 (diff) | |
| download | oslo-db-9fb3c018fc16c8f5b781c119dd3c148ed7954db7.tar.gz | |
Explain paginate_query doesn't provide parameter offset
OFFSET is a terrible thing to use. It seems to work great when you
first use it because your table is only a few hundred rows. six months
later, everyone complains the app is incredibly slow - it's because the
database is being killed doing linear scans through millions of rows
because everyone's doing OFFSET. It not only causes slow and unusable
applications but hurts everyone by adding tons of meaningless work to
the DB load overall.
This pagination function already does the "right" way, which is to order
the rows and use WHERE criteria (See http://use-the-index-luke.com/no-offset).
This commit add docstring to explain why don't need offset.
Co-Authored-By: Mike Bayer <mike_mp@zzzcomputing.com>
Change-Id: I6fdb094085d133c8910415efea2eb44225a66216
| -rw-r--r-- | oslo_db/sqlalchemy/utils.py | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/oslo_db/sqlalchemy/utils.py b/oslo_db/sqlalchemy/utils.py index 97a28c6..f3db1dc 100644 --- a/oslo_db/sqlalchemy/utils.py +++ b/oslo_db/sqlalchemy/utils.py @@ -155,6 +155,11 @@ def paginate_query(query, model, limit, sort_keys, marker=None, marker, then the actual marker object must be fetched from the db and passed in to us as marker. + The "offset" parameter is intentionally avoided. As offset requires a + full scan through the preceding results each time, criteria-based + pagination is preferred. See http://use-the-index-luke.com/no-offset + for further background. + :param query: the query object to which we should add paging/sorting :param model: the ORM model class :param limit: maximum number of items to return |