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This page describes common issues that can occur while using MOLT Fetch and suggests ways to troubleshoot those issues.
Some of the contents of this page are specific to your source database (PostgreSQL, MySQL, or Oracle). Select your source using the dropdown at the top right of this page.

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Fetch issues

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Fetch exits early due to mismatches

When run in none or truncate-if-exists mode, molt fetch exits early in the following cases, and will output a log with a corresponding mismatch_tag and failable_mismatch set to true:
  • A source table is missing a primary key.
  • A source primary key and target primary key have mismatching types.
    These restrictions (missing or mismatching primary keys) can be bypassed with --skip-pk-check.
  • A STRING primary key has a different collation on the source and target.
  • A source and target column have mismatching types that are not allowable mappings.
  • A target table is missing a column that is in the corresponding source table.
  • A source column is nullable, but the corresponding target column is not nullable (i.e., the constraint is more strict on the target).
molt fetch can continue in the following cases, and will output a log with a corresponding mismatch_tag and failable_mismatch set to false:
  • A target table has a column that is not in the corresponding source table.
  • A source column has a NOT NULL constraint, and the corresponding target column is nullable (i.e., the constraint is less strict on the target).
  • A DEFAULT, CHECK, FOREIGN KEY, or UNIQUE constraint is specified on a target column and not on the source column.
The instructions in this section are specific to PostgreSQL source databases. To see instructions for other source database types, select a different option from the dropdown at the top right of this page.

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See also