Zobrazení zdroje stránky Counter postupu procesu pro hromadné operace

Při zpracování hromadných operací není jasné, kolik řádků již bylo zpracováno. PostgreSQL nenabízí, žádný způsob jak se dozvědět, kolik řádek bylo zpracováno:
<pre>
CREATE TABLE source_table(..);
CREATE TABLE destination_table(..);

/* transformation function */
CREATE OR REPLACE FUNCTION to_destination_table(source_table) RETURNS RECORD AS $$ ...

/* transformation */
INSERT INTO destination_table
SELECT (r).*
FROM (SELECT to_destionation_table(_source) r
FROM source _source) x
</pre>
Proto jsem si napsal malou funkci, která pouze počítá počet svých volání a po dosažení nastaveného počtu zobrazí echo:
<pre>
#include "funcapi.h"
#include "utils/lsyscache.h"

PG_FUNCTION_INFO_V1(pst_counter);

Datum pst_counter(PG_FUNCTION_ARGS);

typedef struct
{
   long int iterations;
   int freq;
   Oid typoutput;
} counter_cache;

/*
* raise notice every n call,
* returns input without change
*/
Datum
pst_counter(PG_FUNCTION_ARGS)
{
   Datum value = PG_GETARG_DATUM(0);
   counter_cache *ptr = (counter_cache *) fcinfo->flinfo->fn_extra;

   if (ptr == NULL)
   {
      fcinfo->flinfo->fn_extra = MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
                                                                         sizeof(counter_cache));
      ptr = (counter_cache *) fcinfo->flinfo->fn_extra;
      ptr->iterations = 0;
      ptr->typoutput = InvalidOid;
 
      if (PG_ARGISNULL(1))
         elog(ERROR, "second parameter (output frequency) must not be NULL");

      ptr->freq = PG_GETARG_INT32(1);

      if (!PG_ARGISNULL(2) && PG_GETARG_BOOL(2))
      {
         Oid valtype;
         Oid typoutput;
         bool typIsVarlena;

         valtype = get_fn_expr_argtype(fcinfo->flinfo, 0);
         getTypeOutputInfo(valtype, &typoutput, &typIsVarlena);
         ptr->typoutput = typoutput;
      }
   }

   if (++ptr->iterations % ptr->freq == 0)
   {
      if (!OidIsValid(ptr->typoutput))
      {
         elog(NOTICE, "processed %ld rows", ptr->iterations);
      }
      else
      {
         /* show a processed row, when it's requested */
         if (PG_ARGISNULL(0))
            elog(NOTICE, "processed %ld rows, current value is null", ptr->iterations);
         else
         {
            elog(NOTICE, "processed %ld rows, current value is '%s'", ptr->iterations,
                                                   OidOutputFunctionCall(ptr->typoutput, value));
         }
      }
   }

   PG_RETURN_DATUM(value);
}


CREATE OR REPLACE FUNCTION counter(anyelement, int, bool)
RETURNS anyelement
AS 'MODULE_PATHNAME','pst_counter' LANGUAGE C;
</pre>
Použití je triviální:
<pre>
/* transformation */
INSERT INTO destination_table
SELECT (r).*
FROM (SELECT counter(to_destionation_table(_source), 1000, true) r
FROM source _source) x
</pre>
Výsledek:
<pre>
psql84:convert.sql:183: NOTICE: processed 1230000 rows, current value is '(959674199,"2010-10-25 23:50:29.404568","2010-10-25 23:50:29.491842",,3,501,190000029,XXXXXX,f,9,21)'
psql84:convert.sql:183: NOTICE: processed 1240000 rows, current value is '(959473959,"2010-10-25 19:20:52.498152","2010-10-25 19:20:52.564384",,3,501,189854563,XXXXXX,f,9,23)'
psql84:convert.sql:183: NOTICE: processed 1250000 rows, current value is '(958884965,"2010-10-25 08:53:30.026877","2010-10-25 08:53:30.106039",,3,101,189849045,XXXXXX,f,13,48)'
psql84:convert.sql:183: NOTICE: processed 1260000 rows, current value is '(959483959,"2010-10-25 19:32:02.136491","2010-10-25 19:32:04.070922",,3,500,189969079,XXXXXX,f,9,48)'
psql84:convert.sql:183: NOTICE: processed 1270000 rows, current value is '(959488959,"2010-10-25 19:36:40.691078","2010-10-25 19:36:41.155615",,3,500,189037026,,f,9,)'
psql84:convert.sql:183: NOTICE: processed 1280000 rows, current value is '(959493959,"2010-10-25 19:41:59.21508","2010-10-25 19:41:59.244398",,3,101,189971167,XXXXXX,f,13,42)'
psql84:convert.sql:183: NOTICE: processed 1290000 rows, current value is '(959498959,"2010-10-25 19:49:22.494294","2010-10-25 19:49:22.516124",,3,1010,189971599,XXXXXX,f,9,53)'
</pre>