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Graph/missing-row-locks-overlap-duplication

Pattern

Missing Row Locks Leads to Duplication

missing-row-locks-overlap-duplication

Item selection occurs without locking or lock-state checks, so parallel workers can grab overlapping rows; later updates race, causing duplicate processing and inconsistent counters, especially around increments and transaction isolation boundaries.

Node Details

Public graph metadata

Updated5/4/2026

Connections

30 linked nodes

As long as you lock more than a single thing at a time, you risk deadlocks. — lock more than a single thing at a time. Tension: You hold B waiting for A, they hold A waiting for B. Outcome: one of you has to abort or you're stuck.

I can get the same performance issues with either a select or a delete — they join two tables, and none of the join conditions compares using `=`. Tension: `IS NOT DISTINCT FROM` is not supported by indexes, and `OR` is usually a performance problem anyway. Outcome: the root of your problem are the NULL values.

Clicking any table row always selects the first row, and clicking again toggles off that same first row instead of toggling the clicked row’s selection. Each row effectively behaves like a toggle for the first row.

No ghost row UI indication of how many rows I am reordering

the user is only allowed to drag and drop one row, before the feature becomes broken and stops working. Tension: behavior is wrong.

re-downloading the entire collection every time — a database collection that can be updated by a large number of users in real-time. Tension: the collection is large.

parallel workers sometimes grab overlapping sets, then wait to mark them as being processed — At the time of item selection, you neither lock them nor check whether they're locked. Tension: someone else could've already grabbed a subset of those. Outcome: duplicate their work on the items they happened to share.

the cache doesn't work across processes — workers might be pre-forked. Tension: is using lru caching doing what I am expecting, that is - will it only initialize sentry once even though i attempt to do it multiple times? Outcome: provided it's called within the same process.

sqlite3.OperationalError: database is locked. — I trigger `/session_a` and `/session_b` almost simultaneously. Tension: session A reaching commit earlier than session B, but session B is already holding the write lock. Outcome: A will inevitably fail with a database is locked error.

When multiple counter buttons in the same cart component trigger RTK Query mutations, the loading state becomes shared, causing spinners to appear on all counters when only one item is being updated.

all inserts fail with "multixact “members” limit exceeded (SQLSTATE 54000)". Tension: autovacuum may run for days and not complete in time.

ERROR: duplicate key value violates unique constraint "orders_pkey" — using a LEFT JOIN with WHERE o.order_id IS NULL. Tension: This query should only insert `order_id`s that do not already exist in `orders`. Outcome: Use ON CONFLICT DO NOTHING.

heavy parallel inserts (INSERT INTO ... SELECT ...) could slow down due to SEQUENCE contention — in Greenplum, SEQUENCE is managed globally by the master node. Tension: multiple segments request new IDs in parallel.

Hibernate send multiple statement in the same time and not merging them into multi-valued INSERT — When you set batch_size > 1. Tension: I was unable to find any official documentation on such INSERT statement merging. Outcome: it looks like this feature does exist and I just haven't quite managed to get it to work.

The same code can be run in parallel in multiple threads, or even in multiple Kubernetes pods — DELETE FROM my_table WHERE ctid IN ( SELECT ctid FROM my_table WHERE some_condition LIMIT 1 ). Tension: two threads start fighting for the same record.

Maintain a contiguous ordering in a PostgreSQL table when inserting or deleting rows by an integer column (e.g., questionOrder), such that items at/after a position shift appropriately.

you run the risk of getting duplicates — As several comments to your question pointed out. Tension: This will currently not generate an error because you do not have an appropriate constraint on your table. Outcome: Avoiding duplicates requires a table constraint.

An INSERT...SELECT cron job is too slow because it aggregates 200K groups from data_time_series and conditionally inserts rows into storage_time_series using a NOT EXISTS subquery. The conditional existence check becomes a performance bottleneck.

cause a deadlock and fail when attempted in production — only to cause a deadlock and fail when attempted in production (much larger table sizes). Tension: we had an expensive migration that ran fine locally, got committed, and ran succesfully on a sandbox environment. Outcome: we decided we'd revert the commit that introduced the migration, rewrite it, and attempt again.

Is it possible to lost increment here? Tension: stats.setTotalSold(stats.getTotalSold() + 1); // lost increment? Outcome: Lost increment is impossible with REPEATABLE_READ isolation level (at least in PostgreSQL).

When using jOOQ to translate a JPA-style REST DELETE/UPDATE flow, the user needs to detect whether the target row exists (and/or is accessible) by relying on the number of affected rows. The approach should map 0 deleted rows to HTTP 404, 1 to success, and >1 to an invariant violation.

Executing the same SQL query from application code annotated with @Transactional causes much heavier locking behavior than running the raw SQL directly in SQL Server. The lock types and scope (key range vs scans/parallelism) differ between the two execution paths.

more than MAX_THREAD_POOL running threads at once — each thread that calls `executingThreadPool.add` immediately uses `executingThreadPool.poll`. Tension: your locks don't prevent more than MAX_THREAD_POOL running threads at once. Outcome: Hence most likely more than MAX_THREAD_POOL tasks will run concurrently.

Multiple threads are writing in the file concurrently. — I need to persist this counter because if process get restarted then it counter should start from last count. Tension: I hope there wont be a case when any number shall be skipped or give duplicate value to thread. Outcome: how to reset this key when value reaches to 25k in a thread safe way.

Suppose #0 reads `strong == 1`. That requires: Both `fetch_sub` operations (#2 and #3) have already happened before #0. Tension: Threads that "shouldn't" modify the counter get stuck before performing the release operations that would allow #0 to see a reduced count. Outcome: So the uniqueness test is valid and future-proof.

When using Django transactions with select_for_update inside an atomic block, any insert/write performed after an exception is thrown is rolled back and never persisted to the database.

When two migration SQL files share the same index number. Tension: The other file exists on disk but is silently ignored.

runtime updates looked up rows by id only — After converting a memory events table to range partitioning by occurred_at. Tension: review found two production risks.

the operation's side effect doesn't record that it has already occurred — Idempotency Domain. Tension: re-execution produces duplicate effects.

Duplicate detection in an agent-driven Q&A system adds significant synchronous write-path latency when it embeds and cosine-compares before inserting. Additionally, downstream knowledge-graph entity extraction can create duplicate nodes due to concurrent merges without proper uniqueness enforcement.

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