PostgreSQL uses latches to provide synchronization between different threads accessing shared resources. Latches are lightweight and efficient mechanisms that provide mutual exclusion between threads. Here is a table describing all the PostgreSQL latches, their purpose, and the shared resources they protect:
| Latch name | Purpose | Shared resources protected |
|---|---|---|
| BgWriter | Used by the background writer to write dirty buffers | Access to the shared buffer pool |
| Checkpointer | Used by the checkpoint process to write dirty buffers | Access to the shared buffer pool |
| WALWrite | Used to synchronize WAL writes | Access to the WAL (Write-Ahead Log) buffer |
| WALInsertLock | Used to serialize inserts into the WAL buffer | Access to the WAL buffer |
| WALBufMapping | Used to synchronize access to the WAL buffer mapping | Access to the WAL buffer mapping structure |
| ProcArrayLock | Used to synchronize access to the ProcArray structure | Access to the ProcArray structure, which tracks the status of all processes in the system |
| SInvalRead | Used to synchronize access to shared-invalidation messages | Access to the shared-invalidation message queue |
| SInvalWrite | Used to serialize updates to the shared-invalidation message | Access to the shared-invalidation message queue |
| ProcSignalBarrier | Used to synchronize signaling of processes | Ensures that signals sent to processes are properly delivered |
| BtreeVacuumLock | Used to synchronize access to B-tree pages during vacuum | Access to B-tree pages during vacuum |
| BtreeSplitLock | Used to synchronize access to B-tree pages during splits | Access to B-tree pages during splits |
| BtreeDeleteLock | Used to synchronize access to B-tree pages during deletion | Access to B-tree pages during deletion |
| LWLockTranche | Used to synchronize access to LWLocks | Access to LWLocks, which are used for finer-grained locking of shared resources |
| ProcArrayGroup | Used to synchronize process group changes | Access to the process group structure, which tracks groups of processes and their status |
| SyncScan | Used to synchronize access to sync-scan functionality | Access to the sync-scan functionality, which is used to scan multiple indexes in parallel |
| ExtensionLock | Used to synchronize access to shared extension objects | Access to shared extension objects, which are used to implement extensions in PostgreSQL |
| AutovacuumWorkItem | Used to synchronize access to autovacuum work items | Access to autovacuum work items, which are used to schedule vacuum operations for tables and indexes |
| AsyncioQueueLock | Used to synchronize access to the asyncio queue | Access to the asyncio queue, which is used for asynchronous I/O operations |
| ReplicationSlotAllocationLock | Used to synchronize replication slot allocation | Access to the replication slot allocation process, which is used to allocate replication slots for standby servers |
| ReplicationSlotControlLock | Used to synchronize replication slot control | Access to the replication slot control process, which is used to manage replication slots and cleanup WAL files |
| ReplicationOriginLock | Used to synchronize access to replication origins | Access to the replication origin structure, which is used to track the origins of replication streams |
These latches are a critical part of PostgreSQL’s architecture, providing efficient and effective synchronization of shared resources across multiple threads. It is important to understand the purpose and use of each latch to ensure
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