Finds and fixes application query patterns that inflate Postgres/Neon egress (SELECT *, missing LIMIT, JOIN duplication, in-app aggregation) plus cheap non-prod compute via neon.ts. Use when Neon bills spike, data-transfer costs jump, or list endpoints lack pagination. Not a psql meta-command chair (postgresql-cli) and not a full Neon IaC reference (neon).
Instrucciones de origen · Vista previa de solo lectura
name
neon-postgres-egress-optimizer
description
Finds and fixes application query patterns that inflate Postgres/Neon egress (SELECT *, missing LIMIT, JOIN duplication, in-app aggregation) plus cheap non-prod compute via neon.ts. Use when Neon bills spike, data-transfer costs jump, or list endpoints lack pagination. Not a psql meta-command chair (postgresql-cli) and not a full Neon IaC reference (neon).
Most high Postgres egress bills come from the application fetching more data than it uses. This skill guides you through diagnosing application-side query patterns that cause excessive data transfer from a Postgres database (especially Neon), then applying targeted fixes. It also covers codifying non-production compute cost controls in neon.ts so dev, preview, and CI branches stay cheap by default.
When to Use
Use this skill when any of the following apply:
A user mentions high database bills, unexpected data transfer costs, network transfer charges, or egress spikes.
A user asks "why is my Neon bill so high?" or says "database costs jumped."
You see SELECT * in queries that only use a few columns.
A list endpoint has no LIMIT or pagination.
A high-frequency query targets static or rarely-changing data.
Application code fetches full tables and aggregates in-memory.
A JOIN duplicates wide parent columns across many child rows.
Read access to the target Postgres / Neon database (for diagnostic queries).
The pg_stat_statements extension must be enabled (on Neon it ships by default but may need CREATE EXTENSION).
If you plan to apply the neon.ts infrastructure-as-code changes, the @neon/config npm package and the neon CLI are required.
Procedure
Step 1 — Diagnose with pg_stat_statements
Identify which queries transfer the most data. The primary tool is pg_stat_statements.
1.1 Check extension availability
SELECT1FROM pg_stat_statements LIMIT 1;
If this errors, create the extension:
CREATE EXTENSION IF NOTEXISTS pg_stat_statements;
On Neon, the extension is available by default but may still need this CREATE EXTENSION step.
1.2 Handle empty or stale stats
Stats are cleared when a Neon compute scales to zero and restarts. If stats are empty or the compute recently woke up:
Reset stats to start a clean measurement window:
SELECT pg_stat_statements_reset();
Let the application run under representative traffic for at least one hour.
Return and run the diagnostic queries below.
If the user has stats from a production database, use those. If they have no access to production stats, skip to Step 2 and analyze the codebase directly — code-level patterns are often sufficient to identify the worst offenders.
1.3 Run diagnostic queries
Focus on queries that return many rows, return wide rows (JSONB, TEXT, BYTEA columns), or are called very frequently.
Queries returning the most total rows:
SELECT query, calls, rowsAS total_rows, rows/ calls AS avg_rows_per_call
FROM pg_stat_statements
WHERE calls >0ORDERBYrowsDESC
LIMIT 10;
Queries returning the most rows per execution (poorly scoped SELECTs, missing pagination):
SELECT query, calls, rowsAS total_rows, rows/ calls AS avg_rows_per_call
FROM pg_stat_statements
WHERE calls >0ORDERBY avg_rows_per_call DESC
LIMIT 10;
Most frequently called queries (candidates for caching):
SELECT query, calls, rowsAS total_rows, rows/ calls AS avg_rows_per_call
FROM pg_stat_statements
WHERE calls >0ORDERBY calls DESC
LIMIT 10;
Longest running queries (not a direct egress measure, but helps identify problem queries during a spike):
SELECT query, calls, rowsAS total_rows,
round(total_exec_time::numeric, 2) AS total_exec_time_ms
FROM pg_stat_statements
WHERE calls >0ORDERBY total_exec_time DESC
LIMIT 10;
1.4 Interpret results
Rank findings by estimated egress impact:
High row count + wide rows = biggest egress. A query returning 1,000 rows where each row includes a 50 KB JSONB column transfers ~50 MB per call.
Extreme call frequency on even small queries adds up. A query called 50,000 times/day returning 10 rows each = 500,000 rows/day.
Cross-reference with the schema to identify which columns are wide. Look for JSONB, TEXT, BYTEA, and large VARCHAR columns.
Step 2 — Analyze the codebase
For each query identified in Step 1 — or for each database query in the codebase if no stats are available — check:
Does it select only the columns the response needs?
Does it return a bounded number of rows (LIMIT / pagination)?
Is it called frequently enough to benefit from caching?
Does it fetch raw data that gets aggregated in application code?
Does it use a JOIN that duplicates parent data across child rows?
Step 3 — Apply fixes
Apply the appropriate fix for each problem found. Below are the most common egress anti-patterns and their fixes.
3.1 Unused columns (SELECT *)
Problem: The query fetches all columns but the application only uses a few. Large columns (JSONB blobs, TEXT fields) get transferred over the wire and discarded.
Before:
SELECT*FROM products;
After:
SELECT id, name, price, image_urls FROM products;
3.2 Missing pagination
Problem: A list endpoint returns all rows with no LIMIT. This is an unbounded egress risk — every new row in the table increases data transfer on every request. Flag this regardless of current table size.
This is easy to miss because the application may work fine with small datasets. But at scale, an unpaginated endpoint returning 10,000 rows with even moderate column widths can transfer hundreds of megabytes per day.
Before:
SELECT id, name, price FROM products;
After:
SELECT id, name, price FROM products
ORDERBY id
LIMIT 50OFFSET0;
When adding pagination, check whether the consuming client already supports paginated responses. If not, pick sensible defaults and document the pagination parameters in the API.
3.3 High-frequency queries on static data
Problem: A query is called thousands of times per day but returns data that rarely changes. Every call transfers the same rows from the database. This pattern is only visible from pg_stat_statements — the code itself looks normal.
Look for queries with extremely high call counts relative to other queries. Common examples: configuration tables, category lists, feature flags, user role definitions.
Fix: Add a caching layer between the application and the database so it avoids hitting the database on every request.
3.4 Application-side aggregation
Problem: The application fetches all rows from a table and then computes aggregates (averages, counts, sums, groupings) in application code. The full dataset transfers over the wire even though the result is a small summary.
Fix: Push the aggregation into SQL.
Before: the application fetches entire tables and aggregates in code with loops or .reduce().
After:
SELECT p.category_id,
AVG(r.rating) AS avg_rating,
COUNT(r.id) AS review_count
FROM reviews r
INNERJOIN products p ON r.product_id = p.id
GROUPBY p.category_id;
3.5 JOIN duplication
Problem: A JOIN between a wide parent table and a child table duplicates all parent columns across every child row. If a product has 200 reviews and the product row includes a 50 KB JSONB column, the join sends that 50 KB × 200 = ~10 MB for a single request.
This is distinct from the SELECT * problem. Even if you select only needed columns, a JOIN still repeats the parent data for every child row. The fix is structural: avoid the join entirely.
Before:
SELECT*FROM products
LEFTJOIN reviews ON reviews.product_id = products.id
WHERE products.id =1;
After (two separate queries):
SELECT id, name, price, description, image_urls FROM products WHERE id =1;
SELECT id, user_name, rating, body FROM reviews WHERE product_id =1;
Two queries instead of one JOIN. The product data is fetched once. The reviews are fetched once. No duplication.
The fixes above cut egress (data transferred out of Postgres). The other big non-prod cost lever is compute, and you can codify it durably in neon.ts — Neon's infrastructure-as-code file (see the neon skill for the full reference) — so dev, preview, and CI branches stay cheap by default instead of relying on per-branch flags.
Install the config package:
npm i @neon/config
Create neon.ts:
// neon.tsimport { defineConfig } from"@neon/config/v1";
exportdefaultdefineConfig({
branch: (branch) => {
if (branch.exists || branch.isDefault) return {}; // don't touch prodreturn {
ttl: "7d", // ephemeral branches auto-expire instead of accruing storagepostgres: {
computeSettings: {
autoscalingLimitMinCu: 0.25, // scale to zero when idleautoscalingLimitMaxCu: 1, // cap autoscaling on throwaway branchessuspendTimeout: "5m",
},
},
};
},
});
Apply the configuration:
neon config apply # apply to the current branch (neon deploy is an alias)
This is complementary, not a substitute: query-pattern fixes are what actually reduce egress charges, while these settings keep non-production compute and storage from quietly inflating the same bill. Because neon checkout applies the policy when it creates a branch, new dev/preview branches inherit the cheap profile automatically.
Pitfalls
Neon compute scale-to-zero wipes stats.pg_stat_statements data is cleared when a Neon compute suspends and restarts. If stats look empty, reset and re-measure for at least an hour under representative traffic before drawing conclusions.
Unbounded queries look fine on small datasets. An unpaginated endpoint may pass all tests with 100 rows but transfer hundreds of MB/day once the table grows. Always flag missing LIMIT regardless of current table size.
JOIN duplication is invisible in the code. The query looks reasonable — it selects only needed columns — but the parent row is repeated for every child row. This is a structural problem, not a column-selection problem. The fix is two separate queries, not a better column list.
Column-selection and pagination changes can break clients. Clients may depend on specific fields or full result sets. After applying fixes, verify the API response shape is still compatible.
Caching is not a substitute for query fixes. A cached query that returns SELECT * still transfers full-width rows on cache misses. Fix the query first, then cache.
Do not touch production branch settings in neon.ts. The guard if (branch.exists || branch.isDefault) return {}; exists to protect prod. Removing it can alter production compute settings.
Verification
After applying fixes:
Run existing tests to confirm nothing broke.
Check API responses — make sure the API still returns the same data shape. Column selection and pagination changes can break clients that depend on specific fields or full result sets.
Measure the improvement — if pg_stat_statements data is available:
SELECT pg_stat_statements_reset();
Let traffic run under representative load, then re-run the diagnostic queries from Step 1.3 and compare before/after row counts and call counts.
Confirm neon.ts applied correctly — run neon config apply and verify the branch shows the expected compute settings (autoscaling min 0.25 CU, max 1 CU, suspend timeout 5m, TTL 7d for non-production branches).
Related skills
neon — full reference for Neon infrastructure-as-code (neon.ts), branch lifecycle, and compute settings.
