How to Resolve "Oracle Max Memory Exceeded" in PostgreSQL

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How do I fix the "Oracle max memory exceeded" error in PostgreSQL?

Tuning PostgreSQL memory parameters eliminates “max memory exceeded”‐style errors during large queries or loads.

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Why does PostgreSQL run out of memory?

Large sorts, hashes, or parallel aggregations can exhaust work_mem; many sessions can overrun shared_buffers; huge temp files can hit temp_file_limit. When Linux OOM-kills the backend, the symptom mirrors Oracle’s “max memory exceeded.”

Which parameters control query memory?

work_mem handles per-sort/hash memory, maintenance_work_mem covers VACUUM/CREATE INDEX, shared_buffers manages cache, and temp_file_limit constrains spill size. Adjusting them prevents failures.

How do I inspect current settings?

Run SHOW work_mem; or query pg_settings.Compare the values to available RAM and workload concurrency.

How to increase `work_mem` safely?

Raise it for a single session with SET work_mem = '128MB';. Multiply the value by expected parallel workers to estimate total usage before changing it globally.

Global change example

ALTER SYSTEM SET work_mem = '64MB'; SELECT pg_reload_conf(); applies after reload and affects all new sessions.

How to prevent temp file explosions?

Set temp_file_limit so a single query cannot fill the disk.Example: ALTER SYSTEM SET temp_file_limit = '5GB';

When should I enlarge `shared_buffers`?

Increase it (25-40% of RAM) if cache hit ratio is low. Monitor in pg_stat_database before and after.

Best practices for memory tuning

Scale settings gradually and observe pg_stat_activity.
Grant large work_mem only to reporting roles.
Enable huge pages for kernels >= 4.14 for added stability.

Monitoring tools to catch early warnings

Use pg_stat_kcache or pgBouncer stats to watch per-query memory before the OS intervenes.

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Why How to Resolve "Oracle Max Memory Exceeded" in PostgreSQL is important

How to Resolve "Oracle Max Memory Exceeded" in PostgreSQL Example Usage


-- Run a resource-heavy revenue report without crashing
SET work_mem = '256MB';
SELECT c.name, SUM(oi.quantity * p.price) AS lifetime_value
FROM Customers c
JOIN Orders o  ON o.customer_id = c.id
JOIN OrderItems oi ON oi.order_id = o.id
JOIN Products p ON p.id = oi.product_id
GROUP BY c.name
ORDER BY lifetime_value DESC;

How to Resolve "Oracle Max Memory Exceeded" in PostgreSQL Syntax


ALTER SYSTEM SET work_mem = '<size>';  -- per sort/hash
ALTER SYSTEM SET maintenance_work_mem = '<size>'; -- VACUUM/INDEX
ALTER SYSTEM SET shared_buffers = '<size>'; -- cache
ALTER SYSTEM SET temp_file_limit = '<size>'; -- temp spill cap
-- Example for ecommerce analytics workload
-- Increase work_mem for heavy order reports
ALTER SYSTEM SET work_mem = '128MB';
-- Reload configuration
SELECT pg_reload_conf();

Common Mistakes

Blindly doubling work_mem globally. This can multiply by active sessions and exhaust RAM, leading to crashes. Instead, benchmark and scale gradually.
Editing postgresql.conf without reloading. Changes stay inactive until <code>SELECT pg_reload_conf()</code> or server restart, so the error persists.

Frequently Asked Questions (FAQs)

Does increasing RAM alone fix the error?

Extra RAM helps, but PostgreSQL still needs correct work_mem and shared_buffers settings to use it efficiently.

Can I limit memory per role?

Yes. Create a role-specific config with ALTER ROLE analyst SET work_mem = '256MB'; to isolate heavy reports.

How do I find queries causing spills?

Enable log_temp_files = 0. PostgreSQL logs every file with size, letting you tune the worst offenders.

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