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Thread: [GSoC] Question about returning bytea array

[GSoC] Question about returning bytea array

From
Charles Cui
Date:
Hi Aleksander,

   I have the requirements to return a bytea array for some functions in pg_thrift plugin. 
What I did was similar to the following,

bytea** ret = palloc(len * sizeof(bytea*));
for (int i = 0; i < len; i++) {
   // allocate space
   ret[i] = palloc(size);
   // fill in ret[i]
   ...
}
PG_RETURN_POINTER(ret);
I can verify each ret[i] is correct by logging, but server crash when 
executed PG_RETURN_POINTER(ret). 
So, I am wondering what's the reason of the crash? 
and what's the recommended way (best practice) to construct a return value to be bytea array?

Re: [GSoC] Question about returning bytea array

From
Pavel Stehule
Date:


2018-05-17 7:03 GMT+02:00 Charles Cui <charles.cui1984@gmail.com>:
Hi Aleksander,

   I have the requirements to return a bytea array for some functions in pg_thrift plugin. 
What I did was similar to the following,

bytea** ret = palloc(len * sizeof(bytea*));
for (int i = 0; i < len; i++) {
   // allocate space
   ret[i] = palloc(size);
   // fill in ret[i]
   ...
}
PG_RETURN_POINTER(ret);
I can verify each ret[i] is correct by logging, but server crash when 
executed PG_RETURN_POINTER(ret). 
So, I am wondering what's the reason of the crash? 
and what's the recommended way (best practice) to construct a return value to be bytea array?

You should to set a size of any varlena structure.

check postgresql/src/backend/utils/adt/varlena.c code

When I started with PostgreSQL hacking my often problem was memory allocation in bad (deallocated) context. Good to use own self compiled version of PostgreSQL configured with --enable-cassert option.

Regards

Pavel


Re: [GSoC] Question about returning bytea array

From
Andrew Gierth
Date:
>>>>> "Charles" == Charles Cui <charles.cui1984@gmail.com> writes:

 Charles> I have the requirements to return a bytea array for some
 Charles> functions in pg_thrift plugin.

If you mean you want the return value to be of type bytea[], i.e. an SQL
array of bytea values, then you need to be using construct_array to
construct the result.

-- 
Andrew (irc:RhodiumToad)

Re: [GSoC] Question about returning bytea array

From
Charles Cui
Date:
construct_md_array works for me, thanks for inputs!

2018-05-17 13:42 GMT-07:00 Andrew Gierth <andrew@tao11.riddles.org.uk>:
>>>>> "Charles" == Charles Cui <charles.cui1984@gmail.com> writes:

 Charles> I have the requirements to return a bytea array for some
 Charles> functions in pg_thrift plugin.

If you mean you want the return value to be of type bytea[], i.e. an SQL
array of bytea values, then you need to be using construct_array to
construct the result.

--
Andrew (irc:RhodiumToad)