Hi Team,
We have configured bidirectional replication (but traffic can only flow in one direction) between two data centers (distance: 1000 km, maximum Network latency: 100 ms) with an application TPS (transactions per second) of 700 at maximum.
We are fine with handling up to 500 TPS without observing any lag between the two data centers. However, when TPS increases, we notice a lag in WAL files of over 100 GB (initially, it was 1 TB, but after tuning, it was reduced to 100 GB). During peak times, WAL files are generated at a rate of 4 GB per minute.
All transactions (Tx) take less than 200 ms, with a maximum of 1 second at times (no long-running transactions).
Here are the configured parameters and resources:
- OS: Ubuntu
- RAM: 376 GB
- CPU: 64 cores
- Swap: 32 GB
- PostgreSQL Version: 16.4 (each side has 3 nodes with Patroni and etcd configured)
- DB Size: 15 TB
Parameters configured on both sides:
| Name | Setting | Unit |
|---|
| log_replication_commands | off | |
| logical_decoding_work_mem | 524288 | kB |
| max_logical_replication_workers | 16 | |
| max_parallel_apply_workers_per_subscription | 2 | |
| max_replication_slots | 20 | |
| max_sync_workers_per_subscription | 2 | |
| max_wal_senders | 20 | |
| max_worker_processes | 40 | |
| wal_level | logical | |
| wal_receiver_timeout | 600000 | ms |
| wal_segment_size | 1073741824 | B |
| wal_sender_timeout | 600000 | ms |
Optimizations applied:
- Vacuum freeze is managed during off-hours; no aggressive vacuum is triggered during business hours.
- Converted a few tables to unlogged.
- Removed unwanted tables from publication.
- Partitioned all large tables.
Pending:
- Turning off/tuning autovacuum parameters to avoid triggering during business hours.
Not possible: We are running all tables in a single publication, and it is not possible to separate them.
I would greatly appreciate any suggestions you may have to help avoid logical replication delays, whether through tuning database or operating system parameters, or any other recommendations
