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On Jul 25, 2017 3:38 PM, "Octave J. Orgeron" <octave.orgeron at oracle.com>
wrote:

Hi Michael,

I understand that you want to abstract this completely away inside of
oslo.db. However, the reality is that making column changes based purely on
the size and type of that column, without understanding what that column is
being used for is extremely dangerous. You could end up clobbering a column
that needs a specific length for a value,



Nowhere in my example is the current length truncated.   Also, if two
distinct lengths truly must be maintained we add a field "minimum_length".


prevent

 an index from working, etc.


That's what the indexable flag would achieve.

It

 wouldn't make sense to just do global changes on a column based on the
size.


This seems to be what your patches are doing, however.


There are far more tables that fit in both InnoDB and NDB already than
those that don't. As I've stated many times before, the columns that I make
changes to are evaluated to understand:

1. What populates it?
2. Who consumes it?
3. What are the possible values and required lengths?
4. What is the impact of changing the size or type?
5. Evaluated against the other columns in the table, which one makes the
most sense to adjust?

I don't see a way of automating that and making it maintainable without a
lot more overhead in code and people.


My proposal is intended to *reduce* the great verbosity in the current
patches I see and remove the burden of every project having to be aware of
"ndb" every time a column is added.


If

 we really want to remove the complexity here, why don't we just change the
sizes and types on these handful of table columns so that they fit within
both InnoDB and NDB?



Because that requires new migrations which are a great risk and
inconvenience to projects.

That

 way we don't need these functions and the tables are exactly the same?
That would only leave us with the createtable, savepoint/rollback, etc.
stuff to address which is already taken care of in the ndb module in
oslo.db? Then we just fix the foreign key stuff as I've been doing, since
it has zero impact on InnoDB deployments and if anything ensures things are
consistent. That would then leave us to really focus on fixing migrations
to use oslo.db and pass the correct flags, which is a more lengthy process
than the rest of this.

I don't see the point in trying to make this stuff anymore complicated.


The proposal is to make it simpler than it is right now.

Run though every column change youve proposed and show me which ones don't
fit into my proposed ruleset.   I will add additional declarative flags to
ensure those use cases are covered.





Octave


On 7/25/2017 12:20 PM, Michael Bayer wrote:

> On Mon, Jul 24, 2017 at 5:41 PM, Michael Bayer <mbayer at redhat.com> wrote:
>
>> oslo_db.sqlalchemy.String(255, ndb_type=TINYTEXT) -> VARCHAR(255) for most
>>> dbs, TINYTEXT for ndb
>>> oslo_db.sqlalchemy.String(4096, ndb_type=TEXT) -> VARCHAR(4096) for most
>>> dbs, TEXT for ndb
>>> oslo_db.sqlalchemy.String(255, ndb_size=64) -> VARCHAR(255) on most dbs,
>>> VARCHAR(64) on ndb
>>>
>>> This way, we can override the String with TINYTEXT or TEXT or change the
>>> size for ndb.
>>>
>>>> oslo_db.sqlalchemy.String(255)     -> VARCHAR(255) on most dbs,
>>>> TINYTEXT() on ndb
>>>> oslo_db.sqlalchemy.String(255, ndb_size=64)     -> VARCHAR(255) on
>>>> most dbs, VARCHAR(64) on ndb
>>>> oslo_db.sqlalchemy.String(50)     -> VARCHAR(50) on all dbs
>>>> oslo_db.sqlalchemy.String(64)     -> VARCHAR(64) on all dbs
>>>> oslo_db.sqlalchemy.String(80)     -> VARCHAR(64) on most dbs, TINYTEXT()
>>>> on ndb
>>>> oslo_db.sqlalchemy.String(80, ndb_size=55)     -> VARCHAR(64) on most
>>>> dbs, VARCHAR(55) on ndb
>>>>
>>>> don't worry about implementation, can the above declaration ->
>>>> datatype mapping work ?
>>>>
>>>>
>>>> In my patch for Neutron, you'll see a lot of the AutoStringText() calls
>>> to
>>> replace exceptionally long String columns (4096, 8192, and larger).
>>>
>> MySQL supports large VARCHAR now, OK.   yeah this could be
>> String(8192, ndb_type=TEXT) as well.
>>
> OK, no, sorry each time I think of this I keep seeing the verbosity of
> imports etc. in the code, because if we had:
>
> String(80, ndb_type=TEXT)
>
> then we have to import both String and TEXT, and then what if there's
> ndb.TEXT, the code is still making an ndb-specific decision, etc.
>
> I still see that this can be mostly automated from a simple ruleset
> based on the size:
>
> length <= 64 :    VARCHAR(length) on all backends
> length > 64, length <= 255:   VARCHAR(length) for most backends,
> TINYTEXT for ndb
> length > 4096:  VARCHAR(length) for most backends, TEXT for ndb
>
> the one case that seems outside of this is:
>
> String(255)  where they have an index or key on the VARCHAR, and in
> fact they only need < 64 characters to be indexed.  In that case you
> don't want to use TINYTEXT, right?   So one exception:
>
> oslo_db.sqlalchemy.types.String(255, indexable=True)
>
> e.g. a declarative hint to the oslo_db backend to not use a LOB type.
>
> then we just need oslo_db.sqlalchemy.types.String, and virtually
> nothing except the import has to change, and a few keywords.
>
> What we're trying to do in oslo_db is as much as possible state the
> intent of a structure or datatype declaratively, and leave as much of
> the implementation up to oslo_db itself.
>
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