How to Choose a Database Engine for Your Hosting Stack

If you are asking which database should I use for my website, the honest answer is that you almost certainly want a relational engine with transactions, and you should pick it before you write your schema, not after your traffic doubles. The reason is not fashion. It is that your host's storage, backup tooling, connection limits and replication options are built around one or two engines, and everything else runs as a guest on that host without the same guarantees.

Start by writing down three things: the shape of your data, the shape of your read and write traffic, and what your host actually exposes to you. The third one is the one people skip, and it is the one that forces migrations later.

Start with the data model, not the engine

If your records have relationships that you need to enforce, meaning a row in one table must point at a row that exists in another, you want a relational engine. That means PostgreSQL or MySQL or a compatible fork. Foreign keys, joins and multi statement transactions are the features you are buying, and no document store will give them to you for free. You can fake them in application code, and people do, and then they discover that two concurrent requests can both pass the check and both insert the orphan row.

If your data is genuinely a document, meaning it is fetched whole and written whole, and the fields inside it vary from record to record, a document store is reasonable. A user profile with an open ended settings blob is a document. An order with line items and a payment record is not, because you will want to sum line items across orders and that query is trivial in SQL and painful otherwise.

Time series data, metrics, logs and events are their own category. The access pattern is append heavy, the queries are almost always a range over time, and the correct answer is usually a purpose built store rather than a general one with an index bolted on. Key value caches sit beside your main database, not in place of it. Do not let a cache become your system of record because the cache is fast. Caches lose data on restart by design.

Match the engine to your traffic pattern

Read heavy sites with a modest write rate scale by adding replicas and caching. Write heavy sites scale by partitioning, and partitioning is where engines differ sharply. Know which you are before you choose.

The single most useful diagnostic is your database's own view of what it is doing. On a relational engine you can ask it directly:

SHOW FULL PROCESSLIST;
-- Id  User  Host       db      Command  Time  State      Info
-- 41  app   10.0.0.7   shop    Query    0     Sending    SELECT ...
-- 42  app   10.0.0.9   shop    Sleep    12    (null)     (null)

A pile of Sleep connections means your application is holding connections open and your host's connection limit will bite you before your CPU does. A pile of long running Query rows means you are missing an index or running a scan you did not expect. Both problems look identical from the browser and have completely different fixes.

Connection handling is where hosts constrain you most. Many shared and managed environments cap concurrent connections per database user, and a connection pool that opens one connection per request will exhaust that cap under load. If your host offers a pooler in front of the database, use it. The protocol detail that matters: a pooled connection is not a session. Anything you set with SET at the session level may leak to the next borrower or vanish, depending on the pooling mode. Set your timezone and search path at the connection string level, not with a statement after connect.

Check what your host actually gives you

This is the part that decides the migration question. Ask four things before you commit.

First, the version. A major version number tells you which features exist. Do not build on a feature and then find your host is two major versions behind.

Second, the extension list. On a PostgreSQL host you can enumerate it:

SELECT name, default_version, installed_version
FROM pg_available_extensions
WHERE installed_version IS NOT NULL
ORDER BY name;

If the extension you need is absent from that list, you cannot install it yourself on a managed host, and your choice is now between rewriting the feature and moving hosts.

Third, backups. Not whether backups exist, but whether you can restore one yourself, and how far back they go. Ask for the exact command or button. A backup you cannot restore without opening a support ticket is not a backup you can rely on at three in the morning.

Fourth, replication and failover. Ask whether a read replica is available and what the lag looks like under your write rate. Replica lag is the reason a user posts a comment, reloads, and does not see it. If you serve reads from a replica, your application has to tolerate that, and the fix belongs in the application, not the database.

Storage engine choice inside a relational database matters less than people expect at small scale. The defaults are tuned well. Do not change a storage engine because a blog post said so. Change it when you have a measurement that says the current one is wrong for your workload.

What to do next

Write your three or four hardest queries by hand, before you choose anything, and run them against a local instance of each candidate with a realistic amount of generated data. If a query is awkward in one engine and natural in another, that is your answer, and it is worth more than any comparison table. Then confirm the version, extensions, backup restore path and connection limits with your host in writing, and only then start the schema. Choosing the engine is a one hour decision that saves you a one month migration, and the hour is cheapest right now.