Conflicts
What is a Conflict?
A conflict is a signal to a user that a merge has produced a database that requires further action. The merge algorithm could not infer the state of the database based on the merge rules after the merge. Further input is required to tell Dolt what the resulting merged database should contain.
In Dolt, conflicts can occur on data and schema.
Data
On data, conflicts are detected on a cell-level. If two operations modify the same row, column pair to be different values, a conflict is detected. Primary key values are used to identify rows across versions for the purpose of diff and merge.
A caveat here is columns of JSON type. If two cells of JSON type are modified on both sides of a merge, Dolt will make an attempt to merge the underlying JSON objects. Currently, changes that modify different keys in a JSON object are merged without generating conflicts. Changes that modify the same keys will generate conflicts. Over time, we seek to improve conflict-free merging of JSON objects.
In the case of keyless tables, every column is considered part of the primary key for merge. Thus, conflicts can only be generated in keyless tables if one side of the merge deletes a row and the other side adds the same row.
Schema
Two branches must add, delete or modify a similarly named table, column, foreign key, index or constraint to generate a schema conflict, otherwise the changes are mergeable.
If two branches modify the same named table, column, foreign key, index or check constraint, consult the following tables for conflict detection.
Tables
Left Branch | Right Branch | Caveat | Mergeable |
---|---|---|---|
Add t1 | Add t1 | Same Schema | Yes |
Add t1 | Add t1 | Different Schema | Schema Conflict |
Delete t1 | Delete t1 | Yes | |
Modify t1 | Delete t1 | Schema Conflict | |
Modify t1 | Modify t1 | Same Schema | Yes |
Modify t1 | Modify t1 | Different Schema | Schema Conflict |
Columns
Left Branch | Right Branch | Caveat | Mergeable |
---|---|---|---|
Delete c1 | Delete c1 | Yes | |
Modify c1 | Delete c1 | Schema Conflict | |
Add c1 | Add c1 | Same Type, Same Constraints, Same Data | Yes |
Add c1 | Add c1 | Different Type | Schema Conflict |
Add c1 | Add c1 | Same Type, Different Constraints | Schema Conflict |
Add c1 | Add c1 | Same Type, Same Constraints, Different Data | Data Conflict |
Modify c1 | Modify c1 | Same Type, Same Constraints, Same Data | Yes |
Modify c1 | Modify c1 | Incompatible Type Change | Schema Conflict |
Modify c1 | Modify c1 | Compatible Type Change | Yes |
Modify c1 | Modify c1 | Same Type, Different Constraints | Schema Conflict |
Modify c1 | Modify c1 | Same Type, Same Constraints, Different Data | Data Conflict |
Foreign Keys
Left Branch | Right Branch | Caveat | Mergeable |
---|---|---|---|
Add fk1 | Add fk1 | Same definition | Yes |
Add fk1 | Add fk1 | Different definition | Schema Conflict |
Delete t1 | Delete t1 | Yes | |
Modify fk1 | Delete fk1 | Schema Conflict | |
Modify fk1 | Modify fk1 | Same definition | Yes |
Modify fk1 | Modify fk1 | Different definition | Schema Conflict |
Indexes
Left Branch | Right Branch | Caveat | Mergeable |
---|---|---|---|
Add i1 | Add i1 | Same definition | Yes |
Add i1 | Add i1 | Different definition | Schema Conflict |
Delete i1 | Delete i1 | Yes | |
Modify i1 | Delete i1 | Schema Conflict | |
Modify i1 | Modify i1 | Same definition | Yes |
Modify i1 | Modify i1 | Different definition | Schema Conflict |
Check Constraints
Left Branch | Right Branch | Caveat | Mergeable |
---|---|---|---|
Add ck1 | Add ck1 | Same definition | Yes |
Add ck1 | Add ck1 | Different definition | Schema Conflict |
Delete ck1 | Delete ck1 | Yes | |
Modify ck1 | Delete ck1 | Schema Conflict | |
Modify ck1 | Modify ck1 | Same definition | Yes |
Modify ck1 | Modify ck1 | Different definition | Schema Conflict |
How to use Conflicts
Conflicts signal to the user that a merge is risky. In the event of a conflict, you can either redo the changes on the tip of the branch you are merging into or resolve the conflicts.
In the case of conflict resolution Dolt supports two automated resolution strategies, ours or theirs. You can choose to keep the state of schema or data on the branch you are on or the branch you are merging.
If you would like to manually resolve conflicts, you can set the value of the row that has the conflict to whatever you would like and then resolve the conflict by deleting the corresponding conflict row in dolt_conflicts_<tablename>
.
Difference between Git conflicts and Dolt conflicts
Conflicts are a major divergence from Git in Dolt. Conceptually, Dolt and Git conflicts are similar, but in practice the Dolt conflict management workflow and user interface is very different.
In Dolt, conflicts are stored in the dolt_conflicts
set of tables. Each table in your database has an associated dolt_conflicts
table. For instance if you have a table named docs
, there is a system table named dolt_conflicts_docs
. This replaces the >>>
and <<<
syntax that is inserted into your files in Git when conflicts occur.
Dolt conflicts can occur on schema or data. In Git, conflicts can only occur on lines in files. So Dolt has two types of conflicts whereas Git has one type.
In the case of foreign keys, Dolt can produce invalid merges even after conflicts are resolved. In Dolt, this merge will not be able to be committed until the foreign key violations are resolved. In Git, a repository with no conflict markers is a valid repository and can be committed.
Example
Generating a Conflict
Resolving a Conflict
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