Errors in creating a UDF function in MySQL

Question

I'm trying to create a UDF function for MySQL (a C function executable by MySQL), and I'm running into issues left and right. I'm just going straight into giving you code. I have a file levenshtein.c which includes the following declarations and corresponding implementations:

my_bool     sql_levenshtein_init(UDF_INIT *initid, UDF_ARGS *args, char *message);
void        sql_levenshtein_deinit(UDF_INIT *initid);
longlong    sql_levenshtein(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error);

I compile the file (against std=c99 and for arch=i386, if that's relevant). I copy the created .so file into my mysql plugin folder. I go into mysql and execute the command

mysql> create function sql_levenshtein returns int soname 'levenshtein.so';

Instead of this command successfully creating the function, I receive this error

ERROR 1127 (HY000): Can't find symbol 'sql_levenshtein' in library

In trying to solve the issue, I didn't come up with much useful info. After googling around, I used the command nm to look at the .so file. And I got this output:

00001600 t ___inline_memset_chk
00001870 t ___inline_strcpy_chk
         U ___memset_chk
         U ___stack_chk_fail
         U ___stack_chk_guard
         U ___strcpy_chk
00001220 T _cell_value
         U _free
00001180 T _is_levenshtein_within_normthresh
00001100 T _is_levenshtein_within_thresh
00001460 T _levenshtein
00000cf0 T _levenshtein_k
         U _malloc
00001400 t _minimum
00001660 T _normlevenshtein
000018f0 T _sql_levenshtein
000018c0 T _sql_levenshtein_deinit
00001710 T _sql_levenshtein_init
00001df0 T _sql_levenshtein_within_normthreshold
00001dd0 T _sql_levenshtein_within_normthreshold_deinit
00001d00 T _sql_levenshtein_within_normthreshold_init
00001c00 T _sql_normlevenshtein
00001be0 T _sql_normlevenshtein_deinit
00001b20 T _sql_normlevenshtein_init
         U dyld_stub_binder

Note _sql_levenshtein, so it seems like the function exists. Not sure what else would be helpful. Thanks for your guidance!

Kurt

========= Update in response to comment: Well, for what it's worth, I also did

mysql> create function _sql_levenshtein returns int soname 'levenshtein.so';
ERROR 1127 (HY000): Can't find symbol '_sql_levenshtein' in library

So it doesn't seem like that is the root cause of the issue. Maybe I'm missing something.

sql_levenshtein and _sql_levenshtein are not the same symbol. — Carl Norum
– Carl Norum, Commented Mar 13, 2012 at 23:28
You definitely put the .so file in the right place? Where is it? — Ben Lee
– Ben Lee, Commented Mar 13, 2012 at 23:36
show variables like '%plu%' gives /usr/local/mysql/lib/mysql/plugin, and ls /usr/local/mysql/lib/mysql/plugin | grep leven gives levenshtein.so . — Kurt Spindler
– Kurt Spindler, Commented Mar 13, 2012 at 23:42
@KurtSpindler, I read in the docs somewhere that some systems dynamic linkers don't recognize the file if it doesn't start with "lib". It's an outside chance, but it can't hurt to try renaming it to "liblevenshtein.so" (and updating the so name in the CREATE FUNCTION call accordingly) — Ben Lee
– Ben Lee, Commented Mar 13, 2012 at 23:47
I have one last idea. This was also from the docs: "To be able to use UDFs, you need to link mysqld dynamically. Don't configure MySQL using --with-mysqld-ldflags=-all-static." I guess just make sure that flag's right (probably is, but worth a check I guess) — Ben Lee
– Ben Lee, Commented Mar 14, 2012 at 0:01

user3058610 · Accepted Answer · 2013-12-02 18:55:25Z

1

I don't know if you found your answer, but when you create your function in MySQL, you must use the name of the function you defined. So, if you have a UDF called "my_func_udf" and in your code you have something called My_Func(), in your case you called it:

 longlong sql_levenshtein(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error);

this being the place where all the magic happens, you have to use the name of this function in your create statement, i.e, CREATE FUNCTION My_Func RETURNS (STRING, INTEGER, REAL) SONAME "THE NAME OF YOUR SO FILE".

example from your code stated above:

 CREATE FUNCTION sql_levenshtein RETURNS INTEGER SONAME "levenshtein.so";

You have define something, and then call it something else, this is your mistake.

answered Dec 2, 2013 at 18:55

user3058610

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