MySQL Bugs: #69986: misleading ndb_autoincrement_prefetch

Bug #69986	misleading ndb_autoincrement_prefetch_sz documentation
Submitted:	11 Aug 2013 20:49	Modified:	2 Oct 2013 12:20
Reporter:	Justin Ryan	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Cluster: Cluster (NDB) storage engine	Severity:	S4 (Feature request)
Version:	Any	OS:	Any
Assigned to:	Jon Stephens	CPU Architecture:	Any
Tags:	auto_increment, documentation, ndb_autoincrement_prefetch_sz

Description:
The documentation for ndb_autoincrement_prefetch_sz:

http://dev.mysql.com/doc/refman/5.6/en/mysql-cluster-system-variables.html#sysvar_ndb_auto...

is misleading in this statement:

"The default value for ndb_autoincrement_prefetch_sz is 1, to increase the speed of statements inserting single rows."

This makes it sound like a value of 1 is ideal for the performance of single-row INSERT statements. Actually, increasing the value can significantly improve performance of insert-heavy workloads even when only one row is inserted. 

How to repeat:
n/a

Suggested fix:
Clarify documentation to reflect performance implications of ndb_autoincrement_prefetch_sz. State that the upside of increasing the value is fewer mysqld<->ndbd roundtrips to fetch auto_increment values; the possible downside is likely non-sequential auto_increment values between api nodes.

graph showing benchmark of ndb auto_inc settings

Attachment: chart_2.png (image/png, text), 11.36 KiB.

Hello Justin,

Thank you for the bug report.

Thanks,
Umesh

Thank you for your bug report. This issue has been addressed in the documentation. The updated documentation will appear on our website shortly, and will be included in the next release of the relevant products.

Fixed in mysqldoc rev 36365, by removing the contentious statement.

Closed.