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Update schema changes docs with schema_locked info #21726

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8 changes: 8 additions & 0 deletions src/current/v26.1/online-schema-changes.md
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Expand Up @@ -22,6 +22,14 @@ Schema changes consume additional resources, and if they are run when the cluste
CockroachDB [does not support schema changes within explicit transactions](#schema-changes-within-transactions) with full atomicity guarantees. CockroachDB only supports DDL changes within implicit transactions (individual statements). If a schema management tool uses transactions on your behalf, it should only execute one schema change operation per transaction. <br /><br /> Some tools and applications may be able to workaround CockroachDB's lack of transactional schema changes by [enabling a setting that automatically commits before running schema changes inside transactions](#enable-automatic-commit-before-running-schema-changes-inside-transactions).
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When the [`schema_locked` table storage parameter]({% link {{ page.version.version }}/with-storage-parameter.md %}#storage-parameter-schema-locked) is set to `true`, CockroachDB rejects any schema change statements that target the table.
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The [`create_table_with_schema_locked` session variable]({% link {{ page.version.version }}/set-vars.md %}#create_table_with_schema_locked) (enabled by default in v26.1) automatically sets this storage parameter on every table created in the session.
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Use these features to guarantee that no concurrent schema change is running, which can significantly improve [changefeed]({% link {{ page.version.version }}/change-data-capture-overview.md %}) commit-to-emit latency.
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## How online schema changes work

At a high level, online schema changes are accomplished by using a bridging strategy involving concurrent uses of multiple versions of the schema. The process is as follows:
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