I would like to seek technical review and feedback for an idea. In the long term, I would like InnoDB to support instant ALTER TABLE for a larger set of operations: https://jira.mariadb.org/browse/MDEV-11424 Instant ALTER TABLE of failure-free record format changes Probably one of the most common operations is ADD COLUMN. For that, a ticket had already been filed and some patches exist: https://jira.mariadb.org/browse/MDEV-11369 Instant add column for InnoDB Tencent and Alibaba have ADD COLUMN patches that basically introduce new InnoDB record formats so that each record will carry the number of columns, similar to how ROW_FORMAT=REDUNDANT (the original InnoDB row format) works. A problem with that approach is that we would only be able to support instant ADD COLUMN on data files that already are in a suitable format. The whole purpose of instant ALTER TABLE is to avoid conversions of huge data files. Requiring a conversion before the feature can be used would in my opinion defeat the purpose. I came up with a solution that only requires some changes to the InnoDB page format, not to the record formats: Require each record in a clustered index leaf page to contain the same number of fields (on write, convert the whole page). We can repurpose the previously unused (always 0) field PAGE_MAX_TRX_ID on clustered index leaf pages so that the number of fields in each leaf page can be determined. This is the idea that I posted in MDEV-11369 last week and edited today. As far as I can tell, it should work on any existing data file, and it would be a step towards the full-blown MDEV-11424 in a distant future version of MariaDB. One challenge with the page-at-a-time conversion is that inserting or updating records into a leaf page may require the page to be split into several pages, especially in the case where multiple CHAR(xxx) NOT NULL columns would need to be materialized as a result of the insert or update. Does this seem to make sense to you? I am looking forward to your feedback. Best regards, Marko -- DON’T MISS M|17 April 11 - 12, 2017 The Conrad Hotel New York City https://m17.mariadb.com/ Marko Mäkelä, Lead Developer InnoDB MariaDB Corporation