PostgreSQL Timeout Fix: Long Transaction Issues

Hey guys! Ever run into those pesky errors during long transactions in your PostgreSQL setup? It can be a real headache, especially when you see messages like "server closed the connection unexpectedly." Today, we're diving deep into how wal_sender_timeout and wal_receiver_timeout might be the culprits and how to tackle them.

Understanding the Error: "Server Closed the Connection Unexpectedly"

When you encounter the dreaded "server closed the connection unexpectedly" error, it's like your database is ghosting you mid-conversation. In the context of PostgreSQL replication, this often points to a timeout issue. The error message itself, "Protocol parsing error: server closed the connection unexpectedly," is a strong indicator that the connection between the primary and replica (or in this case, pg2any) was interrupted due to inactivity. This can happen during long-running transactions where no Write-Ahead Logging (WAL) data is sent for a prolonged period.

Diving Deeper into the Logs

Let’s break down the log snippets you shared. We see the initial setup going smoothly:

2025-08-14T16:39:59.385033Z INFO ThreadId(01) pg2any_lib::pg_replication: query : IDENTIFY_SYSTEM, pg_result.status() : PGRES_TUPLES_OK
2025-08-14T16:39:59.385069Z INFO ThreadId(01) pg2any_lib::logical_stream: System identification successful
...
2025-08-14T16:39:59.385861Z INFO ThreadId(01) pg2any_lib::pg_replication: query : START_REPLICATION SLOT "cdc_slot" LOGICAL 0/0 ... , pg_result.status() : PGRES_COPY_BOTH

Everything looks good initially. The system identifies itself, creates a replication slot, and starts the logical replication stream. But then, BAM! We hit this:

2025-08-14T16:40:59.393242Z ERROR ThreadId(04) pg2any_lib::client: Error reading from replication stream: Protocol parsing error: server closed the connection unexpectedly
This probably means the server terminated abnormally before or while processing the request.

This error pops up exactly one minute after a table truncation, suggesting that a long transaction or a period of inactivity might be the culprit. The subsequent warnings about failing to send feedback further confirm that the connection was severed abruptly.

Why Timeouts Matter

Timeouts are crucial for maintaining system health. They prevent idle connections from consuming resources indefinitely. However, they can become problematic when legitimate operations, like long transactions, exceed the timeout threshold. In PostgreSQL, the wal_sender_timeout and wal_receiver_timeout parameters govern these timeouts.

Understanding wal_sender_timeout and wal_receiver_timeout

Okay, let's get down to the nitty-gritty of these timeout settings. These parameters are your first line of defense against zombie connections, but they can also be the villains in our story if not configured correctly. So, what exactly do they do?

wal_sender_timeout: The Primary's Watchdog

The wal_sender_timeout is like the primary server's watchful eye on the replication connection. This setting, defined in milliseconds, dictates how long the primary server (the one sending WAL data) will wait for a response from the replica (or in your case, pg2any) before it decides the connection has gone stale. If the replica doesn't send any feedback within this timeframe, the primary server assumes something's amiss and terminates the connection. Think of it as the primary saying, *