maria-discuss team mailing list archive

[Andy Salnikov <a_salnikov@xxxxxxxxx>]

Hi,

one puzzling feature that we have observed with mariadb is the encoding 
of the result returned from "SHOW CREATE TABLE" query. In our 
Python-based service we issue that query and we expect the result to be 
returned as Python string, that worked OK except that we discovered that 
it breaks for one large/wide table. The query returns Python bytes 
object for that particular table for some reason. I looked at the result 
returned from query and it looks like the data is returned using 
different data type, here is a Python example for two different tables:

This is a regular (narrow) table and it works as expected:
>>> c.execute("SHOW CREATE TABLE `database`.`table1`")
>>> c.description
(('Table', 253, 13, 64, 64, 39, 0), ('Create Table', 253, 375, 1024, 
1024, 39, 0))

253 in second tuple means that this is a MYSQL_TYPE_VAR_STRING type, 
which is converted into Python string.

this is for very wide table:
>>> c.execute("SHOW CREATE TABLE 
`qservTest_case130_qserv`.`deepCoadd_meas`")
>>> c.description
(('Table', 253, 14, 64, 64, 39, 0), ('Create Table', 250, 26235, 78705, 
78705, 39, 0))

in this case type code is 250 which means MYSQL_TYPE_MEDIUM_BLOB, and 
Python (correctly) refuses to understand that this is really a string 
and keeps it as bytes.

It looks like this is triggered by the size of the string, but I could 
not find any document that mentions this unexpected behavior. Is there 
any documentation that explains what to expect in this case? Can this 
behavior be changed with some session or server variable?

To convert that BLOB into string I'd also need to know the encoding for 
its contents, is it supposed to be the same as encoding used to send 
VAR_STRING type or is it some mariadb-internal encoding used by 
information schema?

Thanks,
Andy