pg_xlog_location_diff('','') 這個函式還是比較有用的,在安裝9.1時,沒有建立,需要手動建立,最好建立在 postgres 資料庫下的 public 下。
CREATE OR REPLACE FUNCTION public.pg_xlog_location_diff(text, text)
RETURNS numericLANGUAGE plpgsql
AS $function$
DECLARE
offset1 text;
offset2 text;
xlog1 text;
xlog2 text;
SQL text;
diff text;
BEGIN
/* Extract the Offset and xlog from input in
offset and xlog variables */
offset1=split_part($1,'/',2);
xlog1=split_part($1,'/',1);
offset2=split_part($2,'/',2);
xlog2=split_part($2,'/',1);
/* Prepare SQL query for calculation based on following formula
(FF000000 * xlog + offset) - (FF000000 * xlog + offset)
which gives value in hexadecimal. Since, hexadecimal calculation is cumbersome
so convert into decimal and then calculate the difference */
SQL='SELECT (x'''||'FF000000'||'''::bigint * x'''||xlog1||'''::bigint
+ x'''||offset1||'''::bigint)'||'
-
(x'''||'FF000000'||'''::bigint * x'''||xlog2||'''::bigint
+ x'''||offset2||'''::bigint)';
EXECUTE SQL into diff;
/* Return the value in numeric by explicit casting */
RETURN diff::numeric;
END;
$function$;