Postgres advisory lock path emits SET LOCAL outside a transaction, causing PostgreSQL warnings

[Meryovi]

We are seeing repeated PostgreSQL warnings when running Marten async daemon in HotCold mode across multiple application hosts.

Observed PostgreSQL warning:

WARNING: SET LOCAL can only be used in transaction blocks

Sample:

2026-03-23 14:07:43.867 UTC [946] WARNING:  SET LOCAL can only be used in transaction blocks
2026-03-23 14:07:44.101 UTC [949] WARNING:  SET LOCAL can only be used in transaction blocks
2026-03-23 14:07:48.890 UTC [946] WARNING:  SET LOCAL can only be used in transaction blocks
2026-03-23 14:07:49.163 UTC [949] WARNING:  SET LOCAL can only be used in transaction blocks
2026-03-23 14:07:53.911 UTC [946] WARNING:  SET LOCAL can only be used in transaction blocks
2026-03-23 14:07:54.188 UTC [949] WARNING:  SET LOCAL can only be used in transaction blocks

With additional Npgsql command logging enabled, the nearby statements are:

select last_value from shared.mt_events_sequence;
select last_seq_id, last_updated, transaction_timestamp() as timestamp
from shared.mt_event_progression
where name = 'HighWaterMark';

and then:

SET LOCAL statement_timeout = 0;
SET LOCAL lock_timeout = 0;
SELECT pg_catalog.pg_try_advisory_lock($1) AS result;

This appears to come from the Postgres advisory lock acquisition path used for daemon coordination.

Why this matters:

It produces repeated WARNING entries in PostgreSQL logs
It can create concern that a transaction boundary is broken or that something is misbehaving
In environments with centralized database log monitoring, this looks like an application problem even though behavior seems otherwise functional

Expectation:

Either this path should avoid SET LOCAL when not operating inside a transaction if possible
Or the implementation should use a transactional path if SET LOCAL is required
At minimum, it would be good to know whether this is intended behavior

Environment:

Marten 8.26.0
HotCold async daemon mode
Multiple application hosts active at the same time
PostgreSQL 18 with warning log level enabled

[jeremydmiller]

@Meryovi Try setting StoreOptions.UseMonitoredAdvisoryLock = false; to use the older, Marten version of AdvisoryLock. I'm moving this to a discussion. Some people run into trouble w/ the 3rd party lib, and most don't. We have no idea why yet.

[gp-meryovi]

I tried it but still got the same warning, I just posted a repro. What other effect/s does that setting have, besides triggering the "older" behavior and a third party lib?

[gp-meryovi]

I created a minimal repro for this issue.

You can run it with dotnet run Repro.cs.

I wasn't able to make the warning appear continuously like we see in our containers. My assumption is that this happens because this setup isn't a real cluster, so there's no actual leader election.

That said, the warning still appears regardless of whether UseMonitoredAdvisoryLock is set to true or false.

#!/usr/bin/env dotnet
#:sdk Microsoft.NET.Sdk
#:property TargetFramework=net10.0
#:property LangVersion=preview
#:property Nullable=enable
#:property PublishAot=false

#:package Marten@8.26.1
#:package Testcontainers.PostgreSql@4.11.0
#:package Microsoft.Extensions.Hosting@10.0.5
#:package Microsoft.Extensions.Logging.Console@10.0.5

using DotNet.Testcontainers.Builders;
using JasperFx;
using JasperFx.Events.Daemon;
using JasperFx.Events.Projections;
using Marten;
using Marten.Events.Aggregation;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Testcontainers.PostgreSql;

var postgres = new PostgreSqlBuilder("postgres:18-alpine")
    .WithDatabase("marten_db")
    .WithUsername("postgres")
    .WithPassword("postgres")
    .WithOutputConsumer(Consume.RedirectStdoutAndStderrToConsole())
    .Build();

await postgres.StartAsync();

Console.WriteLine("Postgres started");

var builder = Host.CreateApplicationBuilder(args);

builder.Logging.ClearProviders();
builder.Logging.AddSimpleConsole(options =>
{
    options.SingleLine = true;
    options.TimestampFormat = "HH:mm:ss.fff ";
});
builder.Logging.SetMinimumLevel(LogLevel.Warning);

builder.Services
    .AddMarten(options =>
    {
        options.Connection(postgres.GetConnectionString());
        options.AutoCreateSchemaObjects = AutoCreate.All;
        options.Events.UseMonitoredAdvisoryLock = false; // Doesn't change the result.

        options.Projections.Add<UserProjection>(ProjectionLifecycle.Async);
    })
    .AddAsyncDaemon(DaemonMode.HotCold);

using var host = builder.Build();

await host.StartAsync();

Console.WriteLine("Marten host started. Press any key to stop.");
Console.ReadKey();

await host.StopAsync();
await postgres.DisposeAsync();

public record UserRegistered(Guid UserId, string Name);

public sealed record UserView(Guid Id, string Name);

public sealed class UserProjection : SingleStreamProjection<UserView, Guid>
{
    public static UserView Create(UserRegistered @event) =>
        new(@event.UserId, @event.Name);
}