What column type should be used to store serialized data in a mysql db?

Question

What column type should be used to store serialized data in a mysql db? I know you can use varbinary, blob, text. What\'s considered the best and why?

Edit: I unders

Answer 1

The length limits that @Twisted Pear mentions are good reasons.

Also consider that TEXT and its ilk have a charset associated with them, whereas BLOB data types do not. If you're just storing raw bytes of data, you might as well use BLOB instead of TEXT.

Note that you can still store textual data in a BLOB, you just can't do any SQL operations on it that take charset into account; it's just bytes to SQL. But that's probably not an issue in your case, since it's serialized data with structure unknown to SQL anyway. All you need to do is store bytes and fetch bytes. The interpretation of the bytes is up to your app.

I have also had troubles using LONGBLOB or LONGTEXT using certain client libraries (e.g. PHP) because the client tries to allocate a buffer as large as the largest possible data type, not knowing how large the content will be on any given row until it's fetched. This caused PHP to burst into flames as it tried to allocate a 4GB buffer. I don't know what client you're using, or whether it suffers from the same behavior.

The workaround: use MEDIUMBLOB or just BLOB, as long as those types are sufficient to store your serialized data.

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On the issue of people telling you not to do this, I'm not going to tell you that (in spite of the fact that I'm an SQL advocate). It's true you can't use SQL expressions to perform operations on individual elements within the serialized data, but that's not your purpose. What you do gain by putting that data into the database includes:

• Associate serialized data with other more relational data.
• Ability to store and fetch serialized data according to transaction scope, COMMIT, ROLLBACK.
• Store all your relational and non-relational data in one place, to make it easier to replicate to slaves, back up and restore, etc.