What Keeps a Neon Compute Awake, and What It Costs

We pointed a health check at a Neon compute every 5 minutes, the same as Neon's default scale-to-zero timeout. The compute never suspended. In 40 minutes it took 8 checks, woke once for the first one, and stayed awake the whole time. Over 30 days that is 180 CU-hours at the smallest compute size: about $19 on the Launch plan, $40 on Scale, and on the Free plan it uses up the 100 CU-hour allowance by day 17.

The suspect most people reach for first, an idle connection left open by the app, does not keep a compute awake. We held idle connections, direct and pooled, and the compute suspended every time, a few seconds later than with nothing open. What the suspend did do was cut those connections, including the pooled ones.

This post measures which ordinary clients keep a Neon compute running and which do not, how long a compute takes to suspend, what your app sees when it does, and what each pattern costs per month. Everything runs against real computes in one Neon project, watched through the Neon API, and the scripts are public so you can run them on your own account.

TL;DR

• Idle connections do not stop scale to zero. With a 60-second timeout the compute suspended 66 to 75 seconds after the last query with nothing open, and 81 to 83 seconds with an idle direct or pooled connection held. The suspend dropped every held connection, pooled ones included.
• An open transaction keeps it awake for as long as it stays open. A session left idle in transaction, direct or through the pooler, kept the compute up for the whole 6-minute window, 4 runs out of 4. Setting idle_in_transaction_session_timeout = '30s' let it suspend again.
• A monitoring agent that queries every 20 seconds keeps it awake, even when it only reads pg_stat_database on the postgres database.
• A LISTEN connection does not keep it awake. It is dropped on suspend, and a notification sent after the suspend never reached it (2 of 2 runs).
• Health checks are the expensive one. With the default 5-minute timeout, a check every 5 minutes kept the compute awake for the whole 40-minute run. In our runs the suspend came 312 to 327 seconds after a wake, so each check arrived before it. A check every 6 minutes still kept it awake 90.6% of the time, and every 10 minutes 52.1%.
• A wake adds roughly half a second to a second. End-to-end checks (connect, authenticate, query, close) that woke the compute had medians of 847 to 1,134 ms per run; checks on an awake compute took 308 to 339 ms, from a client 48 ms from the region.

Prerequisites

• A Neon account and an API key (Account settings > API keys). The 60-second timeout used in part of the test needs a plan that lets you change it (Scale); everything with the default 5-minute timeout works on any plan.
• Node.js 22 or newer.
• Basic Postgres knowledge: sessions, transactions, pg_stat_activity.

How Neon decides a compute is idle

Neon's documentation says a compute scales to zero after 5 minutes of inactivity, that you can change the timeout on paid plans, and that a connected logical replication subscriber prevents the suspend. It does not say what counts as activity.

The answer is in the compute's own code. Every compute runs compute_ctl, and its activity monitor checks Postgres every 500 ms. It moves the "last active" time forward when:

1. The totals in pg_stat_database change: the summed active_time (time spent running queries) or the number of sessions, across all databases except postgres and the templates. This catches a query that started and finished between two checks, and every new connection. The code calls this path experimental but says it is on for everyone.
2. Any client backend is in a state other than idle. That includes active (a query is running) and idle in transaction (a transaction is open but doing nothing). Backends of Neon's own cloud_admin role are left out here.
3. An idle backend changed state recently: the latest state_change among idle backends counts as the last activity (the backend check). A connection that ran a query 20 seconds ago and went idle moves the clock to then. Connecting moves it once too, but a connection that then just sits idle does not keep moving it.
4. A logical replication walsender exists, an active logical replication subscription exists, or an autovacuum worker is running.

The control plane reads the last activity time and suspends the compute once the timeout has passed. This is the open-source code at commit f3a0e4f255; the version running in production may differ, which is one more reason to measure.

So the code predicts that an idle connection should not keep a compute awake, and an open transaction should. The rest of this post checks those predictions and puts numbers on them.

How we measured

One Neon project in aws-eu-central-1 running Lakebase Postgres (PostgreSQL 17), every compute fixed at 0.25 CU so CU-hours are easy to read off. Each health-check configuration gets its own branch, and each branch has its own compute, so configurations running side by side do not affect each other. The idle-client scenarios ran one after another on a single branch.

The compute's state comes from GET /projects/{id}/endpoints/{id}, which returns current_state and suspended_at. That is a control-plane call: it never touches the compute, so watching cannot keep it awake. The scripts read it every 2 seconds for the idle clients, every 3 seconds for the health checks, and every 15 seconds for the long unattended watch.

Awake time is an estimate. An awake period starts when a check that found the compute suspended began connecting, and ends at the suspended_at that Neon reports, which is in whole seconds. We checked it against Neon's own record: the project's operations log lists every start_compute and suspend_compute. For the health-check runs, the awake time from the log and from our polling differed by at most half a percentage point. That is a cross-check of the timing, not of the bill.

That check caught one bug of ours. A poll taken a moment after a check woke the compute can still show the previous suspend, and our first summary ended the awake period there. The fix is to ignore a poll whose suspended_at is older than the wake, and even that went wrong at first: Neon's timestamps are whole seconds (17:57:46Z) and ours have milliseconds (17:57:46.649Z), and compared as strings 46Z sorts after 46.649Z. The bug cost two runs 3 to 4 seconds of awake time each, small but in the direction that makes the bill look smaller. The summary now compares timestamps as dates. A review of the draft found a second one: the runner could fire one extra check right at the end of a window. The summary now counts only checks scheduled inside the window, which took one check off two of the runs.

The scripts are split by stage, and each writes JSON lines stamped with a hash of the code that wrote it:

The wake figure in that log is the time to connect and run SELECT 1 at the start of each run. Most runs started right after a suspend, so it is usually a cold start. The last two started on a warm compute: the previous LISTEN run had just woken it to send its test notification, which is why they are near 300 ms.

Idle connections do not keep it awake, and they do not survive the suspend

Stage 1 sets the suspend timeout to 60 seconds, wakes the compute, leaves one kind of client open, and times the suspend from our last query.

What was left open	Runs	Suspended	Seconds from the last query to the suspend
Nothing	3	3 of 3	75, 68, 66
One idle direct connection	3	3 of 3	82, 81, 83
One idle pooled connection (PgBouncer)	3	3 of 3	81, 83, 81
A LISTEN connection	2	2 of 2	83, 79

An idle connection did not stop the suspend. The suspend did come later: the median was 82 seconds with an idle direct connection and 81 with a pooled one, against 68 with nothing open. With three runs per row, all on the same compute one after another, that is an observation we cannot explain, not an established effect. Either way, a compute with a 60-second timeout went to sleep in under a minute and a half with connections still open.

Look at what happened to those connections. Five seconds after each suspend, the script ran SELECT 1 on the connection it had held:

idle direct:  'error' event: Connection terminated unexpectedly
              next query:    Client has encountered a connection error and is not queryable
idle pooled:  'error' event: Connection terminated unexpectedly
              next query:    Client has encountered a connection error and is not queryable

Every held connection was dead, 6 out of 6, pooled ones included, and the LISTEN connections in the last row died the same way. The pooler did not keep its client connections open across the suspend, so a pooled connection string does not protect your app from one.

For most apps the fix is to make sure a dropped connection is handled, not fatal. With node-postgres, use Pool, not a single long-lived Client, and handle the pool's error event. Without a listener, an idle client that loses its socket throws an unhandled error and can crash the process:

import pg from 'pg';

const pool = new pg.Pool({
  connectionString: process.env.DATABASE_URL,
  // Close idle clients before the compute's suspend timeout closes them for you.
  idleTimeoutMillis: 30_000,
});

// An idle client whose socket closed (for example, the compute suspended).
// The pool removes it; this listener stops it from crashing the process.
pool.on('error', (err) => console.warn('idle client dropped:', err.message));

// Retry once on a dropped connection, but only when the caller says the
// statement is safe to run twice.
export async function query(sql, params, { retry = false } = {}) {
  try {
    return await pool.query(sql, params);
  } catch (err) {
    if (retry && /Connection terminated/.test(err.message)) return pool.query(sql, params);
    throw err;
  }
}

The retry is off by default for a reason. When a connection drops, you cannot always tell whether the statement ran before it did, so only retry statements with no side effects or with an idempotency key. A plain read qualifies; an INSERT without a key does not, and neither does a SELECT that calls a function with side effects. The error check also catches only this one message, so treat it as a starting point, not complete coverage.

LISTEN does not keep it awake either

A connection waiting on LISTEN sits in the idle state, so the monitor treats it like any idle connection. Both runs suspended on schedule. After each suspend the script opened a new connection, which woke the compute, and sent NOTIFY keep_awake, 'after-suspend'. The listener never got it, in either run, because its connection had been closed by the suspend.

If you use LISTEN/NOTIFY for cache invalidation or live updates on a compute that scales to zero, the listener must reconnect and run LISTEN again, and it must not assume it saw every notification sent while it was gone. Read the current state after each reconnect.

An open transaction keeps it awake for as long as it stays open

The monitor counts any backend that is not idle as activity, and a session that ran BEGIN and then stopped is idle in transaction. That is the classic leaked transaction: a request handler that checks out a client, starts a transaction, and returns on an error path without COMMIT or ROLLBACK.

What was left open	Runs	Suspended within 6 minutes	After the transaction ended
BEGIN on a direct connection, then nothing	2	0 of 2	suspended 65 and 72 s later
BEGIN on a pooled connection, then nothing	2	0 of 2	suspended 68 and 72 s later
The same, with idle_in_transaction_session_timeout = '30s'	2	2 of 2, 102 and 98 s after the last query

Through the pooler it behaves the same way. In transaction mode, PgBouncer pins a server connection to the client for as long as the transaction is open, so Postgres still sees a backend idle in transaction.

With the timeout set, Postgres ended the leaked session after 30 seconds, and the compute suspended about 70 seconds after that, the same delay as with nothing open. That setting is the one line worth adding to every Neon project that scales to zero, at the database or role level so it applies to every connection:

-- Ends sessions that hold a transaction open with nothing running.
ALTER DATABASE neondb SET idle_in_transaction_session_timeout = '60s';

We checked this form too, with 30s: the database owner role that Neon creates is allowed to run it, a new connection reported 30s without setting anything itself, and a transaction leaked on that connection no longer kept the compute up. It suspended 101 seconds after the last query (scripts/07-database-timeout.mjs).

Pick a value longer than any legitimate pause inside your transactions. A leaked transaction is a bug anyway: it holds locks and stops vacuum from cleaning up. On a compute that scales to zero, it also bills you for every hour it stays open.

A monitoring agent keeps it awake

Monitoring agents such as postgres_exporter keep a connection open and run queries on a timer. We ran the same pattern: one connection to the postgres database, reading pg_stat_database every 20 seconds.

The compute stayed awake for the whole 6-minute window and suspended 63 seconds after the agent stopped. One run only, but it matches the code: each query moves the connection's state_change, and the backend check counts that whichever database the query runs in. Only the pg_stat_database totals leave the postgres database out.

So a database scrape every 15 or 30 seconds keeps the compute awake around the clock. If you want monitoring and scale to zero together, scrape less often than the suspend timeout and accept gaps, or read compute state from the Neon API, which does not wake the compute. That is how we watched compute state for this post without adding database activity.

Health checks: the interval decides everything

Uptime monitors, load balancer probes and Kubernetes readiness probes often run a query to prove the database is reachable. Stage 2 runs exactly that: every N seconds, open a new pooled connection, run SELECT 1, close it. Each configuration gets its own compute, starts from a suspended state, and runs for 12 to 60 minutes while the script records when the compute is awake.

Suspend timeout	Check every	Minutes	Checks	Checks that woke it	Awake	CU-hours per 30 days at 0.25 CU
60 s	30 s	12	24	1	100%	180
60 s	90 s	15	10	10	82.2%	148
60 s	120 s	16	8	8	70.2%	126
60 s	180 s	18	6	6	40.5%	73
300 s	60 s	30	30	1	100%	180
300 s	300 s	40	8	1	100%	180
300 s	360 s	42	7	7	90.6%	163
300 s	420 s	42	6	6	74.7%	135
300 s	600 s	60	6	6	52.1%	94

"Checks that woke it" counts the checks for which the last API reading before the check showed the compute suspended. When that number is 1, only the very first check of the run had to wake the compute, and every later check found it already awake.

The reason a 5-minute check beats a 5-minute timeout is the time between a wake and the suspend that follows it. Where the compute suspended between checks, we can estimate that cycle, from the moment the check started connecting to Neon's suspended_at:

• With the 60-second timeout, a compute woken by a single check suspended 71 to 87 seconds later (24 cycles, median 74 s).
• With the 5-minute timeout, it suspended 312 to 327 seconds later (19 cycles on three computes, median 314 s).

So in our runs, with the default timeout, a check that came within 312 seconds of the previous one always found the compute still up and started the clock again, and a check every 300 seconds kept it up for the whole 40-minute run. That is what we observed, not a guaranteed grace period: the suspend came 12 to 27 seconds after the timeout here, and Neon does not document that gap.

Make the interval a little longer and the compute does get to sleep between checks, but not for long. Every check pays for a full cycle of about 5 minutes and 15 seconds, so every 6 minutes it was awake 90.6% of the time and every 7 minutes 74.7%. A check every 10 minutes woke the compute 6 times out of 6, and each wake kept it up 312 to 313 seconds for a query that took about a second. That is 52% of the hour, for a database that did nothing else.

What a wake costs your users

Letting the compute sleep has a price too: the first request after a quiet stretch waits for the compute to start.

	Median	Max	Checks
Check that found the compute awake	308 to 339 ms per run		59 checks, 3 runs
Check that had to wake it	847 to 1,134 ms per run	1,878 ms	46 wakes, 9 runs
Plain TCP connect to the region (no TLS, no query)	48 ms		10

These are end-to-end times for the whole check: open a new TLS connection, authenticate, run the query and close. That is why even a warm check takes about 300 ms from a client 48 ms away. In three of the runs only the first check woke the compute, so their wake figure is a single sample. Comparing across runs rather than pair by pair, waking the compute added roughly 0.5 to 0.8 seconds, and the slowest wake took 1.9 seconds. None of the 105 checks failed. For context, our Neon free tier benchmarks measured cold starts with a median of 568 ms and a p95 of 1.06 s from a client in the same region, with a different method.

For a health check, an extra second does not matter. For the first user request of the morning it might, and that is the real trade-off you are making when you decide how long the compute may sleep.

What it costs

Neon bills compute in CU-hours: compute size times the hours it runs. A compute kept awake by a light pattern like these sits at its minimum size, so the cost is the minimum CU times the hours awake (real load can scale it up, which costs more). With list prices from Neon's pricing page ($0.106 per CU-hour on Launch, $0.222 on Scale) and the Free plan's 100 CU-hours per project per month, for one 0.25 CU compute over 30 days with nothing else using it:

What keeps it awake	Awake	CU-hours per 30 days at 0.25 CU	Launch	Scale	Free plan
Health check every 1 or 5 min, default timeout	100%	180	$19.08	$39.96	allowance used up after 400 hours, about day 17
Health check every 6 min, default timeout	90.6%	163	$17.28	$36.19	used up around day 19
Health check every 10 min, default timeout	52.1%	94	$9.94	$20.82	fits, with 6 CU-hours left for real traffic
Leaked transaction, monitoring agent every 20 s	100% while it lasts	up to 180	up to $19.08	up to $39.96	as above
Idle connections, LISTEN	suspended normally	no sustained cost observed	none seen	none seen	none seen

On the Free plan, Neon's plans page says that when a project runs out of CU-hours, its compute is suspended until the next billing period. A 5-minute health check on a Free project, starting the month with the full allowance and nothing else using it, does not cost money; it takes the database down for the last 13 days of a 30-day month.

Two things make these numbers bigger in practice:

• Minimum size. We fixed every compute at 0.25 CU. If your compute's autoscaling minimum is 1 CU, multiply by four: an always-awake 1 CU compute is 720 CU-hours a month, $76 on Launch and $160 on Scale.
• Branches. Every branch with a compute has its own suspend timer. A preview environment per pull request, each with its own health check, keeps each preview branch's compute awake. Ten open previews with a 5-minute check are ten always-on computes.

Does Neon wake it on its own?

A May 2026 thread in Neon's GitHub discussions, neondatabase/neon#12900, describes Launch projects at 0.25 CU that each used about 6 CU-hours a day whatever their traffic, which is a compute awake around the clock. One reply blamed check_availability, an operation that Neon's control plane runs to check that a compute can start on a branch. We looked for it in two places.

• Our test project. Stage 3 watched the main branch's compute, which nothing ever connected to, for 3.9 hours after it suspended, reading its state every 15 seconds. It never woke. The project's operations log, read at the end, shows no check_availability and no start_compute for it after the first suspend, and Neon's usage counter for that branch read 368 active seconds, about the six minutes the compute ran after we created the project.
• An older project of ours. Its main compute suspended on 23 September, and we stopped using the project that evening. Its operations log shows one check_availability for that compute on 24 September, 929 ms long, and no start_compute for it afterwards. The compute's suspended_at still reads 23 September. Two weeks later Neon archived the idle branch.

That matches Neon's own description. The operations page says the check verifies that a compute can start, and a 2023 changelog entry says the availability checker runs on 0.25 CU computes and can use pre-started ones. So in these two records, no availability check restarted a suspended compute. That does not rule out other behavior on other projects, and we cannot tell what kept the computes in that thread awake. The patterns that kept ours awake were open transactions, frequent monitoring queries and frequent health checks.

What to change

1. Keep the database out of liveness checks. A liveness probe should check that the process is up, not that Postgres answers. If you must check the database, do it well below the suspend timeout's rate: with the default 5-minute timeout, every 10 minutes still kept the compute awake half the time, so think in hours, not minutes.
2. Check compute state through the API instead of with a query. GET /projects/{project_id}/endpoints/{endpoint_id} returns current_state without waking anything. A monitor that alerts on the API's view of the compute, and only queries the database when a user is actually using it, keeps scale to zero working.
3. Set idle_in_transaction_session_timeout at the database level. It ends leaked transactions, which otherwise keep the compute awake for as long as they stay open, and they are a bug anyway.
4. Scrape metrics less often than the timeout, or not from the database. A monitoring agent that queries every 15 to 30 seconds turns scale to zero off.
5. Expect connections to drop. Idle and LISTEN connections, direct or pooled, were closed when the compute suspended. Use a pool, handle its error event, retry only statements that are safe to repeat, and re-run LISTEN after a reconnect.
6. If you want it awake, say so. On paid plans you can raise the suspend timeout or turn scale to zero off. For a production database with steady traffic, that is often the right call. The compute bill is the same either way, but a setting you chose is explicit and predictable, and a health check that happens to keep the compute up is neither.

What we could not conclude

• Sample sizes are small. Three runs for each idle-connection row, two for the transaction and LISTEN rows, one for the monitoring agent, one for the database-level timeout check, and one run per health-check row. The results agree with the activity-monitor code, which is why we trust them, but the later suspend we saw with idle connections (median 81 to 82 seconds against 68) is not explained, and those scenarios ran one after another on the same compute.
• Open transactions were watched for 6 minutes. The code says such a session counts as activity for as long as it stays open, and all four runs stayed awake for the whole window; we did not run one for hours.
• One region, one compute size. Everything ran in aws-eu-central-1 at 0.25 CU. The time from a wake to the suspend (71 to 87 seconds with a 60-second timeout, 312 to 327 seconds with 5 minutes) may differ in other regions or under load. It also differed between computes in the same project: with the 5-minute timeout, one compute's cycles took 325 to 327 seconds every time while the others took 312 to 314. We do not know why.
• Cost is computed, not billed. Neon's per-branch usage counters (active_time_seconds, compute_time_seconds) read 0 for the short runs when we deleted their branches, and for the longer runs they were well behind our own measurement (for example 988 active seconds against our 1,877), so they seem to update with a delay. We could not check CU-hours against Neon's meter. We checked the awake time against Neon's operations log instead, and converted with list prices.
• Health checks were on a precise schedule, and the gap after the timeout is not documented. A real uptime service has some jitter, and Neon may suspend sooner after the timeout on other computes or in other regions. Either could let a 5-minute check miss now and then; we did not test that.
• We did not test logical replication or autovacuum. The code says both keep a compute awake, and Neon's docs say so for replication subscribers.

Summary

Scale to zero on Neon worked the way the compute's own activity monitor says it should. Idle connections, pooled or direct, and LISTEN connections did not hold a compute up; they were cut when it suspended. Activity did hold it up: a leaked transaction, a monitoring agent, a health check every 5 minutes with the default timeout. That last one is the expensive surprise. It costs a 0.25 CU compute 180 CU-hours a month, which is about $19 on Launch, $40 on Scale, or almost two weeks of downtime on Free.

Run the scripts against your own project to see which of these you have:

git clone https://github.com/The-DevOps-Daily/neon-keep-awake
cd neon-keep-awake && cp .env.example .env   # add a Neon API key
npm install && npm run setup && npm run health-checks