That refers to the total length of the row. InnoDB has a limit of 65k
and NDB is limited to 14k.
A simple example would be the volumes table in Cinder where the row
length goes beyond 14k. So in the IF logic block, I change columns types
that are vastly oversized such as status and attach_status, which by
default are 255 chars. So to determine a more appropriate size, I look
through the Cinder code to find where the possible options/states are
for those columns. Then I cut it down to a more reasonable size. I'm
very careful when I cut the size of a string column to ensure that all
of the possible values can be contained.
In cases where a column is extremely large for capturing the outputs of
a command, I will change the type to Text or TinyText depending on the
length required. A good example of this is in the agents table of
Neutron where there is a column for configurations that has a string
length of 4096 characters, which I change to Text. Text blobs are stored
differently and do not count against the row length.
I've also observed differences between Kilo, Mitaka, and tip where even
for InnoDB some of these tables are getting wider than can be supported.
So in the case of Cinder, some of the columns have been shifted to
separate tables to fit within 65k. I've seen the same thing in Neutron.
So I fully expect that some of the services that have table bloat will
have to cut the lengths or break the tables up over time anyways. As
that happens, it reduces the amount of work for me, which is a good thing.
The most complicated database schemas to patch up are cinder, glance,
neutron, and nova due to the size and complexity of their tables. Those
also have a lot of churn between releases where the schema changes more
often. Other services like keystone, heat, and ironic are considerably
easier to work with and have well laid out tables that don't change much.
Thanks,
Octave
On 2/2/2017 1:25 PM, Mike Bayer wrote:
On 02/02/2017 02:52 PM, Mike Bayer wrote:
But more critically I noticed you referred to altering the names of
columns to suit NDB. How will this be accomplished? Changing a column
name in an openstack application is no longer trivial, because online
upgrades must be supported for applications like Nova and Neutron. A
column name can't just change to a new name, both columns have to exist
and logic must be added to keep these columns synchronized.
correction, the phrase was "Row character length limits 65k -> 14k" -
does this refer to the total size of a row? I guess rows that store
JSON or tables like keystone tokens are what you had in mind here, can
you give specifics ?
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Oracle Linux OpenStack
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