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47 lines
1.5 KiB
Markdown
47 lines
1.5 KiB
Markdown
---
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toc_priority: 12
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toc_title: MaterializedPostgreSQL
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---
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# MaterializedPostgreSQL {#materialize-postgresql}
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## Creating a Table {#creating-a-table}
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``` sql
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CREATE TABLE test.postgresql_replica (key UInt64, value UInt64)
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ENGINE = MaterializedPostgreSQL('postgres1:5432', 'postgres_database', 'postgresql_replica', 'postgres_user', 'postgres_password')
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PRIMARY KEY key;
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```
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## Requirements {#requirements}
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- Setting `wal_level`to `logical` and `max_replication_slots` to at least `2` in the postgresql config file.
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- A table with engine `MaterializedPostgreSQL` must have a primary key - the same as a replica identity index (default: primary key) of a postgres table (See [details on replica identity index](../../database-engines/materialized-postgresql.md#requirements)).
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- Only database `Atomic` is allowed.
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## Virtual columns {#creating-a-table}
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- `_version` (`UInt64`)
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- `_sign` (`Int8`)
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These columns do not need to be added, when table is created. They are always accessible in `SELECT` query.
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`_version` column equals `LSN` position in `WAL`, so it might be used to check how up-to-date replication is.
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``` sql
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CREATE TABLE test.postgresql_replica (key UInt64, value UInt64)
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ENGINE = MaterializedPostgreSQL('postgres1:5432', 'postgres_database', 'postgresql_replica', 'postgres_user', 'postgres_password')
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PRIMARY KEY key;
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SELECT key, value, _version FROM test.postgresql_replica;
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```
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## Warning {#warning}
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1. **TOAST** values convertion is not supported. Default value for the data type will be used.
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