> For the complete documentation index, see [llms.txt](https://docs.vngcloud.vn/vng-cloud-document/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.vngcloud.vn/vng-cloud-document/vdb/relational-database-service-rds/postgresql-cluster/postgresql-cluster-parameters.md).

# Parameters for PostgreSQL Cluster

This page lists the parameters that can be customized through a **DB Configuration Group** when using vDB PostgreSQL Cluster (1 Writer + N Readers).

{% hint style="info" %}

* These parameters apply to PostgreSQL versions **15, 16, 17**.
* **Restart Required** = Yes: Changing this parameter requires a **restart** of the cluster to take effect.
* **Restart Required** = No: Changes are applied immediately without a restart.
* All parameters in the list are modifiable.
  {% endhint %}

{% hint style="warning" %}
**Memory note**: Many parameters directly affect total RAM consumed by PostgreSQL. Setting values too high relative to the node's RAM can cause PostgreSQL to be **OOMKilled**.

**Parameters that affect memory:**

* `max_connections` — when active queries are running, memory increases due to `work_mem` allocated per sort/hash operation, multiplied by the number of concurrent connections
* `shared_buffers` — allocates shared memory at PostgreSQL start and **does not return it to the OS** for the lifetime of the process; setting it too large squeezes the OS page cache and reduces I/O efficiency
* `work_mem` — multiplied by the number of concurrent connections **and** the number of sort/hash operations per query; total actual usage can be very large when many complex queries run in parallel
* `temp_buffers` — temp table buffer per session, multiplied by `max_connections`
* `max_worker_processes` — each background worker consumes additional memory
* `max_wal_senders` — each WAL sender process requires additional memory

Choose values appropriate for the RAM of the node flavour in use.
{% endhint %}

***

### Connections

| Parameter         | Default Value | Allowed Values | Type    | Unit | Description                                              | Restart Required |
| ----------------- | ------------- | -------------- | ------- | ---- | -------------------------------------------------------- | ---------------- |
| `max_connections` | 100           | 25 - 2000      | integer |      | Maximum number of concurrent connections to the database | **Yes**          |

### Memory & Buffers

| Parameter                   | Default Value | Allowed Values    | Type    | Unit | Description                                                  | Restart Required |
| --------------------------- | ------------- | ----------------- | ------- | ---- | ------------------------------------------------------------ | ---------------- |
| `shared_buffers`            | 16384         | 16 - 1073741823   | integer | 8kB  | Memory used as a shared buffer between backend processes     | **Yes**          |
| `work_mem`                  | 4096          | 64 - 2147483647   | integer | kB   | Memory for ORDER BY, JOIN, DISTINCT; uses disk when exceeded | No               |
| `maintenance_work_mem`      | 65536         | 1024 - 2147483647 | integer | kB   | Memory for VACUUM, CREATE INDEX                              | No               |
| `temp_buffers`              | 1024          | 100 - 1073741823  | integer | 8kB  | Buffer memory per session                                    | No               |
| `max_prepared_transactions` | 0             | 0 - 262143        | integer |      | Number of transactions in prepared state                     | **Yes**          |

### Autovacuum

| Parameter                      | Default Value | Allowed Values | Type    | Unit | Description                                    | Restart Required |
| ------------------------------ | ------------- | -------------- | ------- | ---- | ---------------------------------------------- | ---------------- |
| `autovacuum`                   | on            | true / false   | boolean |      | Enable/disable Autovacuum                      | No               |
| `autovacuum_naptime`           | 60            | 1 - 2147483    | integer | s    | Time between two vacuum runs on the same table | No               |
| `autovacuum_vacuum_threshold`  | 50            | 0 - 2147483647 | integer |      | Row update/delete threshold to trigger VACUUM  | No               |
| `autovacuum_analyze_threshold` | 50            | 0 - 2147483647 | integer |      | Row change threshold to trigger ANALYZE        | No               |

### Logging

| Parameter                    | Default Value | Allowed Values  | Type    | Unit | Description                                                                    | Restart Required |
| ---------------------------- | ------------- | --------------- | ------- | ---- | ------------------------------------------------------------------------------ | ---------------- |
| `log_min_duration_statement` | -1            | -1 - 2147483647 | integer | ms   | Log queries that run longer than the specified duration. Value `-1` = disabled | No               |

### Query Planning & Optimization

| Parameter              | Default Value | Allowed Values   | Type    | Unit | Description                                            | Restart Required |
| ---------------------- | ------------- | ---------------- | ------- | ---- | ------------------------------------------------------ | ---------------- |
| `effective_cache_size` | 524288        | 1 - 2147483647   | integer | 8kB  | Estimated disk cache for the planner to choose indexes | No               |
| `random_page_cost`     | 4             | 0 - 1.79769e+308 | float   |      | Cost of random page access                             | No               |
| `seq_page_cost`        | 1             | 0 - 1.79769e+308 | float   |      | Cost of sequential page access                         | No               |
| `enable_seqscan`       | on            | true / false     | boolean |      | Enable/disable sequential scan                         | No               |
| `enable_indexscan`     | on            | true / false     | boolean |      | Enable/disable index scan                              | No               |
| `enable_hashjoin`      | on            | true / false     | boolean |      | Enable/disable hash join                               | No               |

### Locale & Format

| Parameter   | Default Value | Allowed Values  | Type   | Unit | Description              | Restart Required |
| ----------- | ------------- | --------------- | ------ | ---- | ------------------------ | ---------------- |
| `DateStyle` | ISO, MDY      | See table below | string |      | Date/time display format | No               |

**Supported DateStyle values:**

| DateStyle     | Input Example             | Output Example             |
| ------------- | ------------------------- | -------------------------- |
| ISO, DMY      | `01-02-2026` → 1 Feb 2026 | `2026-02-01`               |
| ISO, MDY      | `01-02-2026` → 2 Jan 2026 | `2026-01-02`               |
| ISO, YMD      | `2026-02-01` → 1 Feb 2026 | `2026-02-01`               |
| SQL, DMY      | `01-02-2026` → 1 Feb 2026 | `01/02/2026`               |
| SQL, MDY      | `01-02-2026` → 2 Jan 2026 | `01/02/2026`               |
| SQL, YMD      | `2026-02-01` → 1 Feb 2026 | `2026-02-01`               |
| Postgres, DMY | `01-02-2026` → 1 Feb 2026 | `Fri 01 Feb 00:00:00 2026` |
| Postgres, MDY | `01-02-2026` → 2 Jan 2026 | `Fri 02 Jan 00:00:00 2026` |
| Postgres, YMD | `2026-02-01` → 1 Feb 2026 | `Fri 01 Feb 00:00:00 2026` |
| German, DMY   | `01.02.2026` → 1 Feb 2026 | `01.02.2026`               |
| German, MDY   | `01.02.2026` → 2 Jan 2026 | `02.01.2026`               |
| German, YMD   | `2026.02.01` → 1 Feb 2026 | `01.02.2026`               |

### Asynchronous & Workers

| Parameter              | Default Value | Allowed Values | Type    | Unit | Description                                   | Restart Required |
| ---------------------- | ------------- | -------------- | ------- | ---- | --------------------------------------------- | ---------------- |
| `max_worker_processes` | 32            | 2 - 65536      | integer |      | Maximum number of background worker processes | **Yes**          |

### Replication & WAL

| Parameter            | Default Value | Allowed Values        | Type    | Unit | Description                                                                             | Restart Required |
| -------------------- | ------------- | --------------------- | ------- | ---- | --------------------------------------------------------------------------------------- | ---------------- |
| `wal_level`          | replica       | `replica` / `logical` | string  |      | Level of information written to WAL. Set to `logical` to use Logical Replication or CDC | **Yes**          |
| `max_wal_senders`    | 10            | 10 - 65536            | integer |      | Maximum number of WAL sender processes, used for streaming replication and CDC          | **Yes**          |
| `max_wal_size`       | 2048          | 32 - 2147483647       | integer | MB   | Maximum WAL size before triggering a checkpoint                                         | No               |
| `checkpoint_timeout` | 300           | 30 - 86400            | integer | s    | Maximum time between two automatic checkpoints                                          | No               |

### Transactions & Locking

| Parameter                   | Default Value | Allowed Values  | Type    | Unit | Description                             | Restart Required |
| --------------------------- | ------------- | --------------- | ------- | ---- | --------------------------------------- | ---------------- |
| `max_locks_per_transaction` | 64            | 10 - 2147483647 | integer |      | Maximum number of locks per transaction | **Yes**          |


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