Franck Pachot articles - 250 total
First/Last per Group: PostgreSQL DISTINCT ON and MongoDB DISTINCT_SCAN Performance
On Stack Overflow, the most frequent question for PostgreSQL is: "Select first row in each GROUP BY...
WiredTigerHS.wt: MongoDB MVCC Durable History Store
MongoDB uses the WiredTiger storage engine, which implements Multi‑Version Concurrency Control (MVCC)...
MongoDB Search Index Internals With Luke (Lucene Toolbox GUI Tool)
Previously, I demonstrated MongoDB text search scoring with a simple example, creating a dynamic...
Text Search With MongoDB (BM25 TF-IDF) and PostgreSQL
MongoDB search indexes provide full‑text search capabilities directly within MongoDB, allowing...
Combine Two JSON Collections with Nested Arrays: MongoDB and PostgreSQL Aggregations
Suppose you need to merge two sources of data—both JSON documents containing nested arrays. This was...
MongoDB Multikey Indexes and Index Bound Optimization
Previously, I discussed how MongoDB keeps track of whether indexed fields contain arrays. This...
MongoDB Internals: How Collections and Indexes Are Stored in WiredTiger
WiredTiger is MongoDB’s default storage engine, but what really occurs behind the scenes when...
Resilience of MongoDB's WiredTiger Storage Engine to Disk Failure Compared to PostgreSQL and Oracle
There have been jokes that have contributed to persistent myths about MongoDB's durability. The...
DocumentDB: Comparing Emulation Internals with MongoDB
MongoDB is the leading database for document data modeling, with its Atlas service available on AWS,...
Updates to the Same Value: MongoDB Optimization
In MongoDB, when you update a field to the same value it already holds, the database optimizes the...
PostgreSQL JSONB Size Limits to Prevent TOAST Slicing
In my previous post Embedding Into JSONB Still Feels Like a JOIN for Large Documents, I examined the...
Embedding Into JSONB Still Feels Like a JOIN for Large Documents
Think PostgreSQL with JSONB can replace a document database? It’s a tempting idea: Embed your related...
MongoDB Arrays: Sort Order and Comparison
Arrays in MongoDB are ordered lists of values, and querying them can be confusing because a field...
Why Doesn't Oracle Multi-Value Index Optimize .sort() Like MongoDB Does With its Multi-Key Index?
Until recently, Oracle Database offered very limited options for creating inverted indexes, primarily...
Does PostgreSQL support as much "schema flexibility" as MongoDB? Not for indexing!
Another day, another myth. Someone on Medium claims PostgreSQL offers as much "schema flexibility" as...
PostgreSQL UUID: Bulk insert with UUIDv7 vs UUIDv4
PostgreSQL 18 (currently in beta) introduces a UUID version 7 generation function that features a...
Joining and grouping on array fields in MongoDB may require using $unwind before applying $group or $lookup
Working with nested data in MongoDB simplifies mapping between application objects and database...
MongoDB indexing internals: .showRecordId() and .hint({$natural:1})
You can understand how MongoDB stores documents internally with simple queries that rely on the...
Transaction performance 👉🏻 retry with backoff
A benchmark sponsored by EDB, a PostgreSQL company, in 2019 contributed to the myth that MongoDB...
Why MongoDB skips indexes when flattening or renaming sub-document fields in $project before $match aggregation pipeline
MongoDB is a general-purpose database that offers more than just a JSON datastore. It is recognized...
MongoDB High Availability: Replica Set in a Docker Lab
MongoDB guarantees consistent and durable write operations through write-ahead logging, which...
Lock-Free Wait-on-Conflict and Fail-on-Conflict in MongoDB
Concurrency control in databases has two main modes for handling conflicts. Traditionally, these are...
.hint() in MongoDB is different that SQL optimizer hints: they force indexes
MongoDB sits at the crossroads between SQL, where developers can write queries on a logical model...
Database latency with PostgreSQL and MongoDB: it's the data model that makes it fast
A business transaction ideally involves a single roundtrip to the database. MongoDB allows a single...
![$isArray: [💬,💬,💬] ❌ - Arrays are Argument Lists in MongoDB Aggregation Pipeline](https://media2.dev.to/dynamic/image/width=1000,height=420,fit=cover,gravity=auto,format=auto/https%3A%2F%2Fdev-to-uploads.s3.amazonaws.com%2Fuploads%2Farticles%2F6tbxo1b85isnisay6ctk.png)
$isArray: [💬,💬,💬] ❌ - Arrays are Argument Lists in MongoDB Aggregation Pipeline
If you test $isArray: [42] in MongoDB, it returns false and that's the right answer. If you test...
Sequences in MongoDB
In a previous post about No-gap sequence in PostgreSQL and YugabyteDB, I mentioned that sequences in...
Wildcard Indexes: MongoDB flexibility joins query performance
In SQL databases, we sometimes encounter an Entity-Attribute-Value (EAV) model to work around the...
ALTER TABLE ... ADD COLUMN
MongoDB’s flexible schema allows each document within a collection to have a unique structure, a...
Erik (author of Lucene in Action) is starting a series on search indexes
Introducing "Playing with Search" Series Erik Hatcher ・...
Strong consistency 👉🏻 MongoDB highly available durable writes (Replication)
In the previous post, I used strace to display all calls to write and sync to disk from any MongoDB...