Don't apply defaults to all rows when the added column has no default #855
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Related to dolthub/dolt#2939
When a user was working with a large table, adding a column with no default caused an OOM crash. The crash is a result of the
ADD COLUMNsql statement causing every row to be modified in the table. This is not-expected and a bug. We expect adding a column with no default to only modify the schema and not any Dolt row.The fix is to skip applying defaults to table if the added column has no default. We can call this a "fast" add column since only the schema has to be modified.
In the future, we may also add a "fast" drop column where only the schema is modified. Currently, we modify every row for a
DROP COLUMNstatement. In the "fast" drop scenario, it might be important to ensure values aren't retained acrossADD COLUMNandDROP COLUMNstatements with the same column name. This PR also adds tests to ensure this.