Comment by wvenable
10 hours ago
This really doesn't have anything to do with C#. This is your classic nvarchar vs varchar issue (or unicode vs ASCII). The same thing happens if you mix collations.
I'm not sure why anyone would choose varchar for a column in 2026 unless if you have some sort of ancient backwards compatibility situation.
> I'm not sure why anyone would choose varchar for a column in 2026
The same string takes roughly half the storage space, meaning more rows per page and therefore a smaller working set needed in memory for the same queries and less IO. Also, any indexes on those columns will also be similarly smaller. So if you are storing things that you know won't break out of the standard ASCII set⁰, stick with [VAR]CHARs¹, otherwise use N[VAR]CHARs.
Of course if you can guarantee that your stuff will be used on recent enough SQL Server versions that are configured to support UTF8 collations, then default to that instead unless you expect data in a character set where that might increase the data size over UTF16. You'll get the same size benefit for pure ASCII without losing wider character set support.
Furthermore, if you are using row or page compression it doesn't really matter: your wide-character strings will effectively be UTF8 encoded anyway. But be aware that there is a CPU hit for processing compressed rows and pages every access because they remain compressed in memory as well as on-disk.
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[0] Codes with fixed ranges, etc.
[1] Some would say that the other way around, and “use NVARCHAR if you think there might be any non-ASCIII characters”, but defaulting to NVARCHAR and moving to VARCHAR only if you are confident is the safer approach IMO.
utf16 is more efficient if you have non-english text, utf8 wastes space with long escape sequences. but the real reason to always use nvarchar is that it remains sargeable when varchar parameters are implicitly cast to nvarchar.
I agree with your first point. I've seen this same issue crop up in several other ORMs.
As to your second point. VARCHAR uses N + 2 bytes where as NVARCHAR uses N*2 + 2 bytes for storage (at least on SQL Server). The vast majority of character fields in databases I've worked with do not need to store unicode values.
> The vast majority of character fields in databases I've worked with do not need to store unicode values.
This has not been my experience at all. Exactly the opposite, in fact. ASCII is dead.
Vast majority of text fields I see are coded values that are perfectly fine using ascii, but I deal mostly with English language systems.
Text fields that users can type into directly especially multiline tend to need unicode but they are far fewer.
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Generally if it stores user input it needs to support Unicode. That said UTF-8 is probably a way better choice than UTF-16/UCS-2
The one place UTF-16 massively wins is text that would be two bytes as UTF-16, but three bytes as UTF-8. That's mainly Chinese, Japanese, Korean, etc...
UTF-8 is a relatively new thing in MSSQL and had lots of issues initially, I agree it's better and should have been implemented in the product long ago.
I have avoided it and have not followed if the issues are fully resolved, I would hope they are.
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To complicate matters SQL Server can do Nvarchar compression, but they should have just done UTF-8 long ago:
https://learn.microsoft.com/en-us/sql/relational-databases/d...
Also UTF-8 is actually just a varchar collation so you don't use nvarchar with that, lol?
Since MS SQL Server 2019 varchar supports unicode so now it’s the opposite, you use nvarchar instead of varchar for backwards compatibility reasons.
Yes I have run into this regardless of client language and I consider it a defect in the optimizer.
I wouldn't consider it a defect in the optimizer; it's doing exactly what it's told to do. It cannot convert an nvarchar to varchar -- that's a narrowing conversion. All it can do is convert the other way and lose the ability to use the index. If you think that there is no danger converting an nvarchar that contains only ASCII to varchar then I have about 70+ different collations that say otherwise.
Can you give an example whats dangerous about converting a nvarchar with only ascii (0-127) then using the index otherwise fallback to a scan?
If we simply went to UTF-8 collation using varchar then this wouldn't be an issue either, which is why you would use varchar in 2026, best of both worlds so to speak.
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I think this is a rather pertinent showcase of the danger of outsourcing your thinking to LLMs. This article strongly indicates to me that it is LLM-written, and it's likely the LLM diagnosed the issue as being a C# issue. When you don't understand the systems you're building with, all you can do is take the plausible-sounding generated text about what went wrong for granted, and then I suppose regurgitate it on your LLM-generated portfolio website in an ostensible show of your profound architectural knowledge.
This is not at all just an LLM thing. I've been working with C# and MS SQL Server for many years and never even considered this could be happening when I use Dapper. There's likely code I have deployed running suboptimally because of this.
And it's not like I don't care about performance. If I see a small query taking more than a fraction of a second when testing in SSMS or If I see a larger query taking more than a few seconds I will dig into the query plan and try to make changes to improve it. For code that I took from testing in SSMS and moved into a Dapper query, I wouldn't have noticed performance issues from that move if the slowdown was never particularly large.
This is a common issue, and most developers I worked with are not aware of it until they see the performance issues.
Most people are not aware of how Dapper maps types under the hood; once you know, you start being careful about it.
Nothing to do with LLMs, just plain old learning through mistakes.
actually, LLMs do way better, with dapper the LLM generates code to specify types for strings
Utf8 solved this completely. It works with any length unicode and on average takes up almost as little storage as ascii.
Utf16 is brain dead and an embarrassment
Blame the Unicode consortium for not coming up UTF-8 first (or, really, at all). And for assuming that 65526 code points would be enough for everyone.
So many problems could be solved with a time machine.
The first draft of Unicode was in 1988. Thompson and Pike came up with UTF-8 in 1992, made an RFC in 1998. UTF-16 came along in 1996, made an RFC in 2000.
The time machine would've involved Microsoft saying "it's clear now that USC-2 was a bad idea, so let's start migrating to something genuinely better".
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It gets worse for UTF-16, Windows will let you name files using unpaired surrogates, now you have a filename that exists on your disk that cannot be represented in UTF-8 (nor compliant UTF-16 for that matter). Because of that, there's yet another encoding called WTF-8 that can represent the arbitrary invalid 16-bit values.