![[res_network.png|256]] Network is consumed when Postgres communicates with clients, replicas, or foreign data sources. All client communication goes through the postmaster's socket; replication adds additional streams. - **Visibility**: [[Client]] wait events, [[IPC]] (replication coordination), [[LWLock]] (`SyncRep`) ## Key Concepts ## Client Protocol - **Description**: Postgres uses the pq wire protocol over TCP (or Unix socket). Each backend handles exactly one client connection - **Impact**: `ClientRead` / `ClientWrite` waits mean the backend is blocked waiting on the client — often slow clients or large result sets ## Streaming Replication - **Description**: WAL is streamed from primary to standby via a dedicated `walsender` / `walreceiver` pair. The standby applies WAL continuously - **Impact**: `WalSenderWaitForWAL` (Client), `WalReceiverMain` (Activity), `SyncRep` (LWLock/IPC) waits ## Synchronous Replication - **Description**: With `synchronous_commit = on`, the primary waits for the standby to confirm WAL receipt before acknowledging the transaction commit - **Impact**: `SyncRep` IPC wait on every write transaction; network latency directly adds to transaction commit time ## Logical Replication - **Description**: Higher-level replication of individual table changes, used for selective replication or cross-version migration - **Impact**: `LogicalSyncData`, `LogicalSyncStateChange`, `LogicalApplySendData` IPC waits; `LibPQWalReceiverConnect/Receive` Client waits ## Foreign Data Wrappers / Custom Scans - **Description**: FDWs (`postgres_fdw`, etc.) open their own network connections to remote servers during query execution - **Impact**: `ClientRead`/`ClientWrite` Client waits from the perspective of the remote; latency adds directly to query time ## Key Config Parameters | Parameter | Default | Purpose | | --------------------------- | -------------- | -------------------------------------------------------- | | `max_connections` | 100 | Max simultaneous client connections | | `synchronous_commit` | `on` | Wait for WAL to be confirmed by standby before returning | | `synchronous_standby_names` | (empty) | Which standbys must confirm WAL for synchronous commit | | `wal_sender_timeout` | 60 s | Timeout for WAL sender connections | | `wal_receiver_timeout` | 60 s | Timeout for WAL receiver connections | | `tcp_keepalives_idle` | 0 (OS default) | Seconds before TCP keepalive probes begin | | `tcp_keepalives_interval` | 0 (OS default) | Seconds between keepalive probes | | `tcp_keepalives_count` | 0 (OS default) | Number of keepalive probes before giving up | ## Related Workloads - [[Client]] — all client/replication network wait events - [[IPC]] (`SyncRep`, `LogicalSyncData`, `WalReceiverWaitStart`) - [[LWLock]] (`SyncRep`, `ReplicationSlotControl`)