CREATE OR REPLACE PROCEDURE calculate_discount(...) ... runAlways="true" — Re-executes the changeSet on every single Liquibase run, regardless of whether the content changed. This is appropriate for operations that must be executed every deployment — refreshing statistics, clearing caches, or running a post-deployment validation query. Use sparingly because it adds overhead to every run. The difference: runOnChange triggers on content changes only; runAlways triggers unconditionally. For stored procedures, runOnChange is almost always the better choice because it avoids unnecessary re-execution when nothing changed."> CREATE OR REPLACE PROCEDURE calculate_discount(...) ... runAlways="true" — Re-executes the changeSet on every single Liquibase run, regardless of whether the content changed. This is appropriate for operations that must be executed every deployment — refreshing statistics, clearing caches, or running a post-deployment validation query. Use sparingly because it adds overhead to every run. The difference: runOnChange triggers on content changes only; runAlways triggers unconditionally. For stored procedures, runOnChange is almost always the better choice because it avoids unnecessary re-execution when nothing changed." />

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Database / Liquibase interview questions

What is runOnChange and runAlways in a Liquibase changeSet?

By default, Liquibase runs a changeSet exactly once — it executes it, records it in DATABASECHANGELOG, and never runs it again on subsequent Liquibase runs. Two attributes override this behavior for specific use cases where idempotent re-execution is desired.

runOnChange="true" — Re-executes the changeSet whenever its checksum changes (i.e., whenever the file content changes). Liquibase detects the change by comparing the current file's checksum against the stored MD5SUM in DATABASECHANGELOG. If they differ, it runs the changeSet again and updates the stored checksum. This is useful for objects that are completely replaced rather than incrementally modified — stored procedures, views, functions, and triggers fall into this category.

<changeSet id="sp-calculate-discount" author="frank" runOnChange="true">
    <createProcedure>
        CREATE OR REPLACE PROCEDURE calculate_discount(...)
        ...
    </createProcedure>
</changeSet>

runAlways="true" — Re-executes the changeSet on every single Liquibase run, regardless of whether the content changed. This is appropriate for operations that must be executed every deployment — refreshing statistics, clearing caches, or running a post-deployment validation query. Use sparingly because it adds overhead to every run.

The difference: runOnChange triggers on content changes only; runAlways triggers unconditionally. For stored procedures, runOnChange is almost always the better choice because it avoids unnecessary re-execution when nothing changed.

Which attribute re-executes a changeSet only when its file content has changed?
For which type of database object is runOnChange most appropriate?

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