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Add function pg_xlog_location_diff to help comparisons

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Comparing two xlog locations are useful for example when calculating
replication lag.

Euler Taveira de Oliveira, reviewed by Fujii Masao, and some cleanups
from me
This commit is contained in:
Magnus Hagander
2012-03-04 12:15:24 +01:00
parent 0e5e167aae
commit bc5ac36865
5 changed files with 114 additions and 2 deletions
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90
src/backend/access/transam/xlogfuncs.c
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@ -26,6 +26,7 @@
#include "replication/walreceiver.h"
#include "storage/smgr.h"
#include "utils/builtins.h"
#include "utils/numeric.h"
#include "utils/guc.h"
#include "utils/timestamp.h"
@ -465,3 +466,92 @@ pg_is_in_recovery(PG_FUNCTION_ARGS)
{
PG_RETURN_BOOL(RecoveryInProgress());
}
/*
* Validate the text form of a transaction log location.
* (Just using sscanf() input allows incorrect values such as
* negatives, so we have to be a bit more careful about that).
*/
static void
validate_xlog_location(char *str)
{
#define MAXLSNCOMPONENT 8
int len1,
len2;
len1 = strspn(str, "0123456789abcdefABCDEF");
if (len1 < 1 || len1 > MAXLSNCOMPONENT || str[len1] != '/')
ereport(ERROR,
(errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
errmsg("invalid input syntax for transaction log location: \"%s\"", str)));
len2 = strspn(str + len1 + 1, "0123456789abcdefABCDEF");
if (len2 < 1 || len2 > MAXLSNCOMPONENT || str[len1 + 1 + len2] != '\0')
ereport(ERROR,
(errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
errmsg("invalid input syntax for transaction log location: \"%s\"", str)));
}
/*
* Compute the difference in bytes between two WAL locations.
*/
Datum
pg_xlog_location_diff(PG_FUNCTION_ARGS)
{
text *location1 = PG_GETARG_TEXT_P(0);
text *location2 = PG_GETARG_TEXT_P(1);
char *str1,
*str2;
XLogRecPtr loc1,
loc2;
Numeric result;
/*
* Read and parse input
*/
str1 = text_to_cstring(location1);
str2 = text_to_cstring(location2);
validate_xlog_location(str1);
validate_xlog_location(str2);
if (sscanf(str1, "%X/%X", &loc1.xlogid, &loc1.xrecoff) != 2)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("could not parse transaction log location \"%s\"", str1)));
if (sscanf(str2, "%X/%X", &loc2.xlogid, &loc2.xrecoff) != 2)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("could not parse transaction log location \"%s\"", str2)));
/*
* Sanity check
*/
if (loc1.xrecoff > XLogFileSize)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("xrecoff \"%X\" is out of valid range, 0..%X", loc1.xrecoff, XLogFileSize)));
if (loc2.xrecoff > XLogFileSize)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("xrecoff \"%X\" is out of valid range, 0..%X", loc2.xrecoff, XLogFileSize)));
/*
* result = XLogFileSize * (xlogid1 - xlogid2) + xrecoff1 - xrecoff2
*/
result = DatumGetNumeric(DirectFunctionCall2(numeric_sub,
DirectFunctionCall1(int8_numeric, Int64GetDatum((int64) loc1.xlogid)),
DirectFunctionCall1(int8_numeric, Int64GetDatum((int64) loc2.xlogid))));
result = DatumGetNumeric(DirectFunctionCall2(numeric_mul,
DirectFunctionCall1(int8_numeric, Int64GetDatum((int64) XLogFileSize)),
NumericGetDatum(result)));
result = DatumGetNumeric(DirectFunctionCall2(numeric_add,
NumericGetDatum(result),
DirectFunctionCall1(int8_numeric, Int64GetDatum((int64) loc1.xrecoff))));
result = DatumGetNumeric(DirectFunctionCall2(numeric_sub,
NumericGetDatum(result),
DirectFunctionCall1(int8_numeric, Int64GetDatum((int64) loc2.xrecoff))));
PG_RETURN_NUMERIC(result);
}