Logical Replication Delay

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:*

1. Vacuum freeze is managed during off-hours; no aggressive vacuum is
triggered during business hours.
2. Converted a few tables to unlogged.
3. Removed unwanted tables from publication.
4. Partitioned all large tables.

*Pending:*

1. 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

--
Thanks & Regards,
Ram.