spin-wait-blob.pgc

/*
 *  Synopsis:
 *	Spin wait on a blob in an SQL table, up to a timeout seconds.
 *  Description:
 *	Spin wait for a blob to appear in an SQL table, backing off
 *	exponentially until more seconds than timeout has expired.
 *	Execute the following SQL query for existence:
 *
 *		SELECT EXISTS (
 *	  	  SELECT
 *			<column_name>
 *		    FROM
 *			<table_name>
 *		    WHERE
 *			<column_name> = <blob>::udig
 *	  	)
 *
 *  Usage:
 *	spin-wait-blob <table> <row> <trys> <blob udig>
 *  Exit Status:
 *	0	blob appeared
 *	1	blob never appeared
 *	2	invocation error
 *	3	sql warning
 *	4	sql error
 *  Note:
 *	Find a clearer way to assemble the query than appending with
 *	_strcat().
 *
 *	For fast syncing environments, adding a back-off algorithm might
 *	be reasonable.
 *
 *		spin-wait-blob plus1 ...
 *		spin-wait-blob double
 *
 *	spin-wait-blob is a desparate but effective hack.  hopefully pg logical
 *	replication will alleviate the need for wating on sunk data to appear
 *	in the database.
 */

static char progname[] = "spin-wait-blob";

#define EXIT_OK		0
#define EXIT_NO_BLOB	1
#define EXIT_BAD_INVO	2
#define EXIT_SQLWARN	3
#define EXIT_SQLERROR	4

#define COMMON_NEED_DIE2
#include "common.c"

#define COMMON_ECPG_NEED_SQL_ERROR
#define COMMON_ECPG_NEED_SQL_WARNING
#include "common-ecpg.c"

#include <stdlib.h>

int
main(int argc, char **argv)
{
	int try_count;
	char *table_name, *column_name, *blob;
EXEC SQL BEGIN DECLARE SECTION;
	bool blob_exists;
	char query[4096];
EXEC SQL END DECLARE SECTION;

	if (argc != 5)
		die(EXIT_BAD_INVO, "wrong number of arguments");

	table_name = argv[1];
	column_name = argv[2];
	blob = argv[4];

	/*
	 *  Parse the number of trys.
	 */
	{
		char *trys = argv[3];
		size_t len = strlen(trys);

		if (len < 1 || len > 19)
			die2(EXIT_BAD_INVO,"trys not > 0 and < 20 chars", trys);
		try_count = atoi(trys);
		if (try_count <= 0)
			die2(EXIT_BAD_INVO, "negative number of trys", trys);
	}

	EXEC SQL WHENEVER SQLERROR CALL _ecpg_sql_error(
		(struct _ecpg_sql_state_fault *)0
	);
	EXEC SQL WHENEVER SQLWARNING CALL _ecpg_sql_warning(
		(struct _ecpg_sql_state_fault *)0
	);
	EXEC SQL CONNECT TO default;

	/*
	 *  Build the query:
	 *
	 *	SELECT EXISTS (
	 *	  SELECT
	 *		<column_name>
	 *	    FROM
	 *		<table_name>
	 *	    WHERE
	 *		<column_name> = <blob>::udig
	 *	  )
	 */
	query[0] = 0;
	_strcat(query, sizeof query, "SELECT EXISTS (SELECT ");
	_strcat(query, sizeof query, column_name);
	_strcat(query, sizeof query, " FROM ");
	_strcat(query, sizeof query, table_name);
	_strcat(query, sizeof query, " WHERE ");
	_strcat(query, sizeof query, column_name);
	_strcat(query, sizeof query, " = '");
	_strcat(query, sizeof query, blob);
	_strcat(query, sizeof query, "'::udig)");

	EXEC SQL PREPARE get_blob FROM :query;

AGAIN:
	EXEC SQL EXECUTE get_blob INTO :blob_exists;

	if (blob_exists)
		_exit(EXIT_OK);

	if (--try_count <= 0)
		_exit(EXIT_NO_BLOB);
	sleep(1);
	goto AGAIN;
}