I have a django app that uses MySQL as the database backend. It's been running for a few days now, and I'm up to ID 5000 in some tables already.
I'm concerned about what will happen when I overflow the datatype.
Is there anyway to tell the auto increment to start over at some point? My data is very volatile, so when I do overflow the ID, there is no possible way that ID 0, or anywhere near that will still be in use.
Depending on whether you're using an unsigned integer or not and which version of MySQL you're running, you run the rink of getting nasty negative values for the primary key or (worse) the row simply won't be inserted and will throw an error.
That said, you can easily change the size/type of the integer in MySQL using an ALTER command to preemptively stop this from happening. The "standard" size for an INT being used as a primary key is an INT(11), but the vast majority of DB applications don't need anything nearly that large. Try a MEDIUMINT.
MEDIUMINT - The signed range is –8388608 to 8388607. The unsigned range is 0 to 16777215
As compared to....
INT or INTEGER - The signed range is –2147483648 to 2147483647. The unsigned range is 0 to 4294967295
There's also the BIGINT, but to be honest you've probably got much larger scalability issues than your data types to worry about if you have a table with > 2 billion rows :)
Well, the default 32bit INT goes up to about 2 billion. At 5000 IDs per day, that's about 1000 years till overflow. I don't think you have to worry yet...
Related
In working on a project, where:
A dataset is collected every 10 seconds, which is stored in an SQlite file on an server.
After being processed, the data is sent to an SQL-Database every 5 minutes.
Afterwards the data in the SQlite file, which isn't needed anymore, gets deleted.
The collecting of the data continues and at the moment the id doens't get reset.
I didn't get how much an integer in SQLite can store according to the documentation (https://www.sqlite.org/datatype3.html).
In MySQL-Databases the maximum value of an interger column is 2.147.483.647. If my script would run for 10 years the id would be 31.449.600. Although this would be much lower less than the maximum, I wondered,
if there is any problem with storing high values in SQlite.
Could this affect the performance?
That page mentions that integer numbers can be stored in up to 8 bytes, i.e., 64 bits.
As mentioned elsewhere, this means that the largest allowed integer is 9,223,372,036,854,775,807.
An integer in SQLite can store values up to 9223372036854775807 (8 Bytes signed so 63 bits as 1 bit is for the sign), which is the same as a MySQL BIGINT (which is in addition to the Standard INT).
This question already has answers here:
Identity increment is jumping in SQL Server database
(6 answers)
Closed 9 years ago.
Ok so I used this code to make the table:
CREATE TABLE Clients
(
ID int IDENTITY(1,1) PRIMARY KEY,
NAME varchar(20) NOT NULL,
BALANCE int NOT NULL,
)
And it worked good for the first few times and after when i add a new record it gives it like an random id:
I dont really know what the problem is so you might tell me?
This is all perfectly normal. Microsoft added sequences in SQL Server 2012
By default when you create a SEQUENCE you can either supply CACHE size. Caching is used to increase performance for applications that use sequence objects by minimizing the number of disk IOs that are required to generate sequence numbers.
To fix this issue, you need to make sure, you add a NO CACHE option in sequence creation / properties like this.
CREATE SEQUENCE TEST_Sequence
AS INT
START WITH 1
INCREMENT BY 1
MINVALUE 0
NO MAXVALUE
NO CACHE
Sequence number
use trace flag 272 - this will cause a log record to be generated
for each generated identity value. The performance of identity
generation may be impacted by turning on this trace flag.
use a sequence generator with the NO CACHE setting
(http://msdn.microsoft.com/en-us/library/ff878091.aspx)
Identity column value suddenly jumps to 1001 in sql server
Simple question. I have tried searching on Google and after about 6 searches, I figured it would be faster here.
How big is an int in SQL?
-- table creation statement.
intcolumn INT(N) NOT NULL,
-- more table creation statement.
How big is that INT(N) element? What's its range? Is it 2^N or is it N Bytes long? (2 ^ 8N)? Or even something else I have no idea about?
It depends on the database. MySQL has an extension where INT(N) means an INT with a display width of 4 decimal digits. This information is maintained in the metadata.
The INT itself is still 4 bytes, and values 10000 and greater can be stored (and probably displayed, but this depends how the application uses the result set).
Why would someone use numeric(12, 0) datatype for a simple integer ID column? If you have a reason why this is better than int or bigint I would like to hear it.
We are not doing any math on this column, it is simply an ID used for foreign key linking.
I am compiling a list of programming errors and performance issues about a product, and I want to be sure they didn't do this for some logical reason. If you follow this link:
http://msdn.microsoft.com/en-us/library/ms187746.aspx
... you can see that the numeric(12, 0) uses 9 bytes of storage and being limited to 12 digits, theres a total of 2 trillion numbers if you include negatives. WHY would a person use this when they could use a bigint and get 10 million times as many numbers with one byte less storage. Furthermore, since this is being used as a product ID, the 4 billion numbers of a standard int would have been more than enough.
So before I grab the torches and pitch forks - tell me what they are going to say in their defense?
And no, I'm not making a huge deal out of nothing, there are hundreds of issues like this in the software, and it's all causing a huge performance problem and using too much space in the database. And we paid over a million bucks for this crap... so I take it kinda seriously.
Perhaps they're used to working with Oracle?
All numeric types including ints are normalized to a standard single representation among all platforms.
There are many reasons to use numeric - for example - financial data and other stuffs which need to be accurate to certain decimal places. However for the example you cited above, a simple int would have done.
Perhaps sloppy programmers working who didn't know how to to design a database ?
Before you take things too seriously, what is the data storage requirement for each row or set of rows for this item?
Your observation is correct, but you probably don't want to present it too strongly if you're reducing storage from 5000 bytes to 4090 bytes, for example.
You don't want to blow your credibility by bringing this up and having them point out that any measurable savings are negligible. ("Of course, many of our lesser-experienced staff also make the same mistake.")
Can you fill in these blanks?
with the data type change, we use
____ bytes of disk space instead of ____
____ ms per query instead of ____
____ network bandwidth instead of ____
____ network latency instead of ____
That's the kind of thing which will give you credibility.
How old is this application that you are looking into?
Previous to SQL Server 2000 there was no bigint. Maybe its just something that has made it from release to release for many years without being changed or the database schema was copied from an application that was this old?!?
In your example I can't think of any logical reason why you wouldn't use INT. I know there are probably reasons for other uses of numeric, but not in this instance.
According to: http://doc.ddart.net/mssql/sql70/da-db_1.htm
decimal
Fixed precision and scale numeric data from -10^38 -1 through 10^38 -1.
numeric
A synonym for decimal.
int
Integer (whole number) data from -2^31 (-2,147,483,648) through 2^31 - 1 (2,147,483,647).
It is impossible to know if there is a reason for them using decimal, since we have no code to look at though.
In some databases, using a decimal(10,0) creates a packed field which takes up less space. I know there are many tables around my work that use that. They probably had the same kind of thought here, but you have gone to the documentation and proven that to be incorrect. More than likely, I would say it will boil down to a case of "that's the way we have always done it, because someone one time said it was better".
It is possible they spend a LOT of time in MS Access and see 'Number' often and just figured, its a number, why not use numeric?
Based on your findings, it doesn't sound like they are the optimization experts, and just didn't know. I'm wondering if they used schema generation tools and just relied on them too much.
I wonder how efficient an index on a decimal value (even if 0 scale is set) for a primary key compares to a pure integer value.
Like Mark H. said, other than the indexing factor, this particular scenario likely isn't growing the database THAT much, but if you're looking for ammo, I think you did find some to belittle them with.
In your citation, the decimal shows precision of 1-9 as using 5 bytes. Your column apparently has 12,0 - using 4 bytes of storage - same as integer.
Moreover, INT, datatype can go to a power of 31:
-2^31 (-2,147,483,648) to 2^31-1 (2,147,483,647)
While decimal is much larger to 38:
- 10^38 +1 through 10^38 - 1
So the software creator was actually providing more while using the same amount of storage space.
Now, with the basics out of the way, the software creator actually limited themselves to just 12 numbers or 123,456,789,012 (just an example for place holders not a maximum number). If they used INT they could not scale this column - it would go up to the full 31 digits. Perhaps there is a business reason to limit this column and associated columns to 12 digits.
An INT is an INT, while a DECIMAL is scalar.
Hope this helps.
PS:
The whole number argument is:
A) Whole numbers are 0..infinity
B) Counting (Natural) numbers are 1..infinity
C) Integers are infinity (negative) .. infinity (positive)
D) I would not cite WikiANYTHING for anything. Come on, use a real source! May as well be http://MyPersonalMathCite.com
What happen when SQL Server 2005 happen to reach the maximum for an IDENTITY column? Does it start from the beginning and start refilling the gap?
What is the behavior of SQL Server 2005 when it happen?
You will get an overflow error when the maximum value is reached. If you use the bigint datatype with a maximum value of 9,223,372,036,854,775,807 this will most likely never be the case.
The error message you will get, will look like this:
Msg 220, Level 16, State 2, Line 10
Arithmetic overflow error for data type tinyint, value = 256.
(Source)
As far as I know MS SQL provides no functionality to fill the identity gaps, so you will either have to do this by yourself or change the datatype of the identity column.
In addition to this you can set the start value to the smallest negative number, to get an even bigger range of values to use.
Here is a good blog post about this topic.
It will not fill in the gaps. Instead inserts will fail until you change the definition of the column to either drop the identity and find some other way of filling in the gaps or increase the size (go from int to bigint) or change the type of the data (from int to decimal) so that more identity values are available.
You will be unable to insert new rows and will receive the error message listed above until you fix the problem. You can do this a number of ways. If you still have data and are using all the id's below the max, you will have to change the datatype. If the data is getting purged on a regular basis and you have a large gap that is not going to be used, you can reseed the identity number to the lowest number in that gap. For example,at a previous job,we were logging transactions. We had maybe 40-50 million per month, but we were purging everything older than 6 months, so every few years, the identity would get close to 2 Billion, but we would have nothing with an id below 1.5 billion, so we would reseed back to 0. Again it's possible that neither of these will work for you and you will have to find a different solution.
If the identity column is an Integer, then your max is 2,147,483,647. You will get an overflow error if you exceed it.
If you think this is a risk, just use the BIGINT datatype, which gives you up to 9,223,372,036,854,775,807. Can't imagine a database table with that many rows.
Further discussion here. (Same link as xsl mentioned).
In the event that you do hit the maximum number for you identity column, you can move the data from that table into a secondary table with a bigger identity column type and specify the starting value for that new identity value to be the maximum of the previous type. The new identity values will continue from that point.
If you delete "old values" from time to time you just need to reset the seed using
DBCC CHECKIDENT ('MyTable', RESEED, 0);