> For the complete documentation index, see [llms.txt](https://docs.greennode.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.greennode.ai/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** |