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‎docs/limitations.md‎

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# MyRocks limitations
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Compared to InnoDB, the MyRocks storage engine lacks the following features:
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## Online DDL limitations
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* MyRocks has limited support for [Online DDL operations](https://dev.mysql.com/doc/refman/8.0/en/innodb-online-ddl.html) due to the lack of atomic DDL. As a result the schema changes are more restricted compared to InnoDB.
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MyRocks has limited support for [Online DDL operations](https://dev.mysql.com/doc/refman/8.0/en/innodb-online-ddl.html) due to the lack of atomic DDL. As a result the schema changes are more restricted compared to InnoDB.
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* `Traditional MyRocks DDL behavior`
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### Traditional MyRocks DDL behavior
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| Operation type | Examples | ALGORITHM |
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|---------------------|--------------------------------------------------|-----------------------------|
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| Index operations | `ADD INDEX`, `DROP INDEX`, `RENAME INDEX` | `INPLACE` (always) |
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| Column changes | `ADD COLUMN`, `DROP COLUMN`, `MODIFY COLUMN` | `COPY` (full table rebuild) |
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| Metadata changes | `RENAME TABLE`, some `RENAME COLUMN` operations | May be `INSTANT` |
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| Operation type | Examples | ALGORITHM |
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|---------------------|--------------------------------------------------|-----------------------------|
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| Index operations | `ADD INDEX`, `DROP INDEX`, `RENAME INDEX` | `INPLACE` (always) |
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| Column changes | `ADD COLUMN`, `DROP COLUMN`, `MODIFY COLUMN` | `COPY` (full table rebuild) |
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| Metadata changes | `RENAME TABLE`, some `RENAME COLUMN` operations | May be `INSTANT` |
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**Note:** MyRocks does not support atomic DDL. Even metadata-only operations may require a full table rebuild, depending on the nature of the change.
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**Note:** MyRocks does not support atomic DDL. Even metadata-only operations may require a full table rebuild, depending on the nature of the change.
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* As of `Percona Server for MySQL 8.0.25-15`, MyRocks supports `INPLACE` partition management for certain operations:
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### Partition management support
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```sql
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ALTER TABLE t1 DROP PARTITION p1, ALGORITHM=INPLACE;
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ALTER TABLE t1 ADD PARTITION (PARTITION p2 VALUES LESS THAN (MAXVALUE)), ALGORITHM=INPLACE;
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```
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The aforementioned operations no longer require a full table rebuild. However, operations that modify partitioning schemes, such as changing `VALUES LESS THAN`, still fall back to the `COPY` algorithm.
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As of `Percona Server for MySQL 8.0.25-15`, MyRocks supports `INPLACE` partition management for certain operations:
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**Note:** Dropping a partition permanently deletes any data stored in it unless that data is reassigned to another partition.
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```sql
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ALTER TABLE t1 DROP PARTITION p1, ALGORITHM=INPLACE;
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ALTER TABLE t1 ADD PARTITION (PARTITION p2 VALUES LESS THAN (MAXVALUE)), ALGORITHM=INPLACE;
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```
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The aforementioned operations no longer require a full table rebuild. However, operations that modify partitioning schemes, such as changing `VALUES LESS THAN`, still fall back to the `COPY` algorithm.
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**Note:** Dropping a partition permanently deletes any data stored in it unless that data is reassigned to another partition.
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### Instant DDL support
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As of `Percona Server for MySQL 8.0.42-33`, MyRocks introduces limited support for Instant DDL, which is disabled by default and controlled via configuration variables.
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* As of `Percona Server for MySQL 8.0.42-33`, MyRocks introduces limited support for Instant DDL, which is disabled by default and controlled via configuration variables.
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To enable specific types of instant operations, use the following configuration options:
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To enable specific types of instant operations, use the following configuration options:
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| Configuration variable | Enables Instant DDL for | ALGORITHM (internal only) |
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|------------------------|--------------------------|----------------------------|
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| [`rocksdb_enable_instant_ddl_for_append_column=ON`](variables.md#rocksdb_enable_instant_ddl_for_append_column) | `ALTER TABLE ... ADD COLUMN` | `INSTANT` |
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| [`rocksdb_enable_instant_ddl_for_column_default_changes=ON`](variables.md#rocksdb_enable_instant_ddl_for_column_default_changes) | `ALTER/MODIFY COLUMN … DEFAULT` | `INSTANT` |
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| [`rocksdb_enable_instant_ddl_for_drop_index_changes=ON`](variables.md#rocksdb_enable_instant_ddl_for_drop_index_changes) | `ALTER TABLE ... DROP INDEX` | `INSTANT` |
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| [`rocksdb_enable_instant_ddl_for_table_comment_changes=ON`](variables.md#rocksdb_enable_instant_ddl_for_table_comment_changes) | `ALTER TABLE ... COMMENT` | `INSTANT` |
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| Configuration variable | Enables Instant DDL for | ALGORITHM (internal only) |
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|------------------------|--------------------------|----------------------------|
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| [`rocksdb_enable_instant_ddl_for_append_column=ON`](variables.md#rocksdb_enable_instant_ddl_for_append_column) | `ALTER TABLE ... ADD COLUMN` | `INSTANT` |
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| [`rocksdb_enable_instant_ddl_for_column_default_changes=ON`](variables.md#rocksdb_enable_instant_ddl_for_column_default_changes) | `ALTER/MODIFY COLUMN … DEFAULT` | `INSTANT` |
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| [`rocksdb_enable_instant_ddl_for_drop_index_changes=ON`](variables.md#rocksdb_enable_instant_ddl_for_drop_index_changes) | `ALTER TABLE ... DROP INDEX` | `INSTANT` |
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| [`rocksdb_enable_instant_ddl_for_table_comment_changes=ON`](variables.md#rocksdb_enable_instant_ddl_for_table_comment_changes) | `ALTER TABLE ... COMMENT` | `INSTANT` |
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**Note:** MyRocks does **not support `ALGORITHM=INSTANT`** in SQL syntax. These operations behave like Instant DDL **internally**, but only if the respective configuration variables are enabled.
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**Note:** MyRocks does **not support `ALGORITHM=INSTANT`** in SQL syntax. These operations behave like Instant DDL **internally**, but only if the respective configuration variables are enabled.
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## Unsupported InnoDB features in MyRocks
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* [ALTER TABLE .. EXCHANGE PARTITION](https://dev.mysql.com/doc/refman/8.0/en/partitioning-management-exchange.html).
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