MySQL Bugs: #43174: Some system variables need documentation on value constraints

Bug #43174	Some system variables need documentation on value constraints
Submitted:	25 Feb 2009 10:33	Modified:	20 Jul 2009 19:08
Reporter:	Patrick Crews	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: Documentation	Severity:	S3 (Non-critical)
Version:	5.0+	OS:	Any
Assigned to:	MC Brown	CPU Architecture:	Any
Tags:	Docs, system variables, variable size limits, variables

Description:
Certain system variables have size limitations / constraints that are not properly documented.

For example:
range_alloc_block_size,query_alloc_block_size, query_prealloc_size, transaction_alloc_block_size, and transaction_prealloc_size  all seem to be constrained to multiples of 1024, but this is not documented.

How to repeat:
In a running mysql server, perform the following commands:

SET @@query_alloc_block_size=1024*17+2;
SHOW VARIABLES LIKE 'query_alloc_block_size';

You should see that the returned value is:
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| query_alloc_block_size | 17408 | 
+------------------------+-------+

17408 = 1024*17

Suggested fix:
Document such constraints in the relevant sections of the manual.

I suspect the limitations are reasonable given what these variables represent.  However, it is always good to let people know about any constraints they must live with.

Fixed.