SQL Server Int or BigInt database table Ids_问答_开发者

I am writing a new program and it will require a database (SQL Server 2008). Everything I am running now for the system is 64-bit, which brings me to this question. For all of the Id columns in various tables, should I make them all INT or BIGINT? I doubt the sys开发者_如何转开发tem will ever surpass the INT range but it is a possibility within some of the larger financial tables I suppose. It seems like INT is the standard though...

OK, let's do a quick math recap:

INT is 32-bit and gives you basically 4 billion values - if you only count the values larger than zero, it's still 2 billion. Do you have this many employees? Customers? Products in stock? Orders in the lifetime of your company? REALLY?
BIGINT goes way way way beyond that. Do you REALLY need that?? REALLY?? If you're an astronomer, or into particle physics - maybe. An average Line of Business user? I strongly doubt it

Imagine you have a table with - say - 10 million rows (orders for your company). Let's say, you have an Orders table, and that OrderID which you made a BIGINT is referenced by 5 other tables, and used in 5 non-clustered indices on your Orders table - not overdone, I think, right?

10 million rows, by 5 tables plus 5 non-clustered indices, that's 100 million instances where you are using 8 bytes each instead of 4 bytes - 400 million bytes = 400 MB. A total waste... you'll need more data and index pages, your SQL Server will have to read more pages from disk and cache more pages.... that's not beneficial for your performance - plain and simple.

PLUS: What most programmer's don't think about: yes, disk space it dirt cheap. But that wasted space is also relevant in your SQL Server RAM memory and your database cache - and that space is not dirt cheap!

So to make a very long post short: use the smallest type of INT that really suits your need; if you have 10-20 distinct values to handle - use TINYINT. If you need an order table, I believe INT should be PLENTY ENOUGH - BIGINT is only a waste of space.

Plus: should any of your tables really ever get close to reaching 2 or 4 billion rows, you'll still have plenty of time to upgrade your table to a BIGINT ID, if that's really needed.......

You should use the smallest data type that makes sense for the table in question. That includes using smallint or even tinyint if there are few enough rows.

You'll save space on both data and indexes and get better index performance. Using a bigint when all you need is a smallint is similar to using a varchar(4000) when all you need is a varchar(50).

Even if the machine's native word size is 64 bits, that only means that 64-bit CPU operations won't be any slower than 32-bit operations. Most of the time, they also won't be faster, they'll be the same. But most databases are not going to be CPU bound anyway, they'll be I/O bound and to a lesser extent memory-bound, so a 50%-90% smaller data size is a Very Good Thing when you need to perform an index scan over 200 million rows.

Here is an article with some real answers on performance... I prefer to answer questions with hard numbers if possible... If you click the following link at least up to a million records you will find a negligible difference in disk usage....

http://www.sqlservercentral.com/articles/Performance+Tuning/2753/

Personally I do feel that using the appropriate ID size is important,but also consider the fact that you may have a table that has a ton of activity over time. It is not that your storing a massive amount of data, but that the key value has grown due to the nature of being auto-incremented (deletes and inserts occurring over time).

Consider a file repository on a community site, or the id of the user comments on a community site multi-tenant application.

I understand that most developers are building systems that will never touch millions of records, but it is important to note that there are reasons that a bigint is required, and I am still not convinced that when you are designing a schema that you do not know the potential growth for that you should not attempt to anticipate the future and consider using a bigint if you feel that the potential is there to exceed the max value of int as the id value grows.

The alignment of 32 bit numbers with x86 architecture or 64 bit with x64 architecture is called data structure alignment

This has no meaning for data in a database because here it's things disk space, data cache and table/index architecture that affect performance (as mentioned in other answers).

Remember, it's not the CPU accessing the data as such. It's the DB engine code (which may be aligned, but who cares?) that runs on the CPU and manipulates your data. When/if your data goes through the CPU it certainly won't be in the same on-disk structures.

Other people already gave compelling answers for 32-bit IDs.

For some applications 64-bit IDs do make more sense.

If you want to guarantee that IDs are unique across a cluster of databases - 63-bits for IDs can be very convenient. With 32 bits it's very difficult to distribute generation of IDs across servers in a cluster; or across data centers. While with 64 bits you have enough room to play with that you can conveniently generate IDs across servers without locking and still guarantee uniqueness.

For example see Twitter Snowflake, and Instagram Engineering's blog post on "Sharding & IDs at Instagram". Both provide good reasons why 63 or 64 bits make more sense for their IDs than 32-bit counters.

You should judge each table individually as to what datatype would meet the needs for each one. If an INTEGER would meet the needs of a particular table, use that. If a SMALLINT would be sufficient, use that. Use the datatype that will last, without being excessive.

The first answer is the naive answer for anyone not working with TB size databases or tables with constant and high volume inserts. In any decent sized database you will run into problems with INT at some stage in its lifetime. Use BIGINT if you have to as it will save a lot of hassle further down the line. I have seen companies hit the INT issue after only a year of data and where reseeding was not an option it caused massive downtime. Also in long running systems (10 years+) where the system was not expected to still be used it has been hit even with moderate sized databases that purge old data. It is much better to use GUID in most cases where large amounts of data are expected but barring that use BIGINT if required.