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Add stats for min, max, mean, stddev times to pg_stat_statements.

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The new fields are min_time, max_time, mean_time and stddev_time.

Based on an original patch from Mitsumasa KONDO, modified by me. Reviewed by Petr Jelínek.
This commit is contained in:
Andrew Dunstan
2015-03-27 15:43:22 -04:00
parent 8816af65e4
commit 717f709532
6 changed files with 170 additions and 7 deletions
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87
contrib/pg_stat_statements/pg_stat_statements.c
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@ -115,7 +115,8 @@ typedef enum pgssVersion
{
PGSS_V1_0 = 0,
PGSS_V1_1,
PGSS_V1_2
PGSS_V1_2,
PGSS_V1_3
} pgssVersion;
/*
@ -136,6 +137,10 @@ typedef struct Counters
{
int64 calls; /* # of times executed */
double total_time; /* total execution time, in msec */
double min_time; /* minimim execution time in msec */
double max_time; /* maximum execution time in msec */
double mean_time; /* mean execution time in msec */
double sum_var_time; /* sum of variances in execution time in msec */
int64 rows; /* total # of retrieved or affected rows */
int64 shared_blks_hit; /* # of shared buffer hits */
int64 shared_blks_read; /* # of shared disk blocks read */
@ -274,6 +279,7 @@ void _PG_fini(void);
PG_FUNCTION_INFO_V1(pg_stat_statements_reset);
PG_FUNCTION_INFO_V1(pg_stat_statements_1_2);
PG_FUNCTION_INFO_V1(pg_stat_statements_1_3);
PG_FUNCTION_INFO_V1(pg_stat_statements);
static void pgss_shmem_startup(void);
@ -320,6 +326,7 @@ static char *generate_normalized_query(pgssJumbleState *jstate, const char *quer
int *query_len_p, int encoding);
static void fill_in_constant_lengths(pgssJumbleState *jstate, const char *query);
static int comp_location(const void *a, const void *b);
static inline double sqrtd(const double x);
/*
@ -1215,6 +1222,32 @@ pgss_store(const char *query, uint32 queryId,
e->counters.calls += 1;
e->counters.total_time += total_time;
if (e->counters.calls == 1)
{
e->counters.min_time = total_time;
e->counters.max_time = total_time;
e->counters.mean_time = total_time;
}
else
{
/*
* Welford's method for accurately computing variance.
* See <http://www.johndcook.com/blog/standard_deviation/>
*/
double old_mean = e->counters.mean_time;
e->counters.mean_time +=
(total_time - old_mean) / e->counters.calls;
e->counters.sum_var_time +=
(total_time - old_mean) * (total_time - e->counters.mean_time);
/* calculate min and max time */
if (e->counters.min_time > total_time)
e->counters.min_time = total_time;
if (e->counters.max_time < total_time)
e->counters.max_time = total_time;
}
e->counters.rows += rows;
e->counters.shared_blks_hit += bufusage->shared_blks_hit;
e->counters.shared_blks_read += bufusage->shared_blks_read;
@ -1259,7 +1292,8 @@ pg_stat_statements_reset(PG_FUNCTION_ARGS)
#define PG_STAT_STATEMENTS_COLS_V1_0 14
#define PG_STAT_STATEMENTS_COLS_V1_1 18
#define PG_STAT_STATEMENTS_COLS_V1_2 19
#define PG_STAT_STATEMENTS_COLS 19 /* maximum of above */
#define PG_STAT_STATEMENTS_COLS_V1_3 23
#define PG_STAT_STATEMENTS_COLS 23 /* maximum of above */
/*
* Retrieve statement statistics.
@ -1271,6 +1305,16 @@ pg_stat_statements_reset(PG_FUNCTION_ARGS)
* expected API version is identified by embedding it in the C name of the
* function. Unfortunately we weren't bright enough to do that for 1.1.
*/
Datum
pg_stat_statements_1_3(PG_FUNCTION_ARGS)
{
bool showtext = PG_GETARG_BOOL(0);
pg_stat_statements_internal(fcinfo, PGSS_V1_3, showtext);
return (Datum) 0;
}
Datum
pg_stat_statements_1_2(PG_FUNCTION_ARGS)
{
@ -1360,6 +1404,10 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
if (api_version != PGSS_V1_2)
elog(ERROR, "incorrect number of output arguments");
break;
case PG_STAT_STATEMENTS_COLS_V1_3:
if (api_version != PGSS_V1_3)
elog(ERROR, "incorrect number of output arguments");
break;
default:
elog(ERROR, "incorrect number of output arguments");
}
@ -1519,6 +1567,23 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
values[i++] = Int64GetDatumFast(tmp.calls);
values[i++] = Float8GetDatumFast(tmp.total_time);
if (api_version >= PGSS_V1_3)
{
values[i++] = Float8GetDatumFast(tmp.min_time);
values[i++] = Float8GetDatumFast(tmp.max_time);
values[i++] = Float8GetDatumFast(tmp.mean_time);
/*
* Note we are calculating the population variance here, not the
* sample variance, as we have data for the whole population,
* so Bessel's correction is not used, and we don't divide by
* tmp.calls - 1.
*/
if (tmp.calls > 1)
values[i++] =
Float8GetDatumFast(sqrtd(tmp.sum_var_time / tmp.calls));
else
values[i++] = Float8GetDatumFast(0.0);
}
values[i++] = Int64GetDatumFast(tmp.rows);
values[i++] = Int64GetDatumFast(tmp.shared_blks_hit);
values[i++] = Int64GetDatumFast(tmp.shared_blks_read);
@ -1541,6 +1606,7 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
Assert(i == (api_version == PGSS_V1_0 ? PG_STAT_STATEMENTS_COLS_V1_0 :
api_version == PGSS_V1_1 ? PG_STAT_STATEMENTS_COLS_V1_1 :
api_version == PGSS_V1_2 ? PG_STAT_STATEMENTS_COLS_V1_2 :
api_version == PGSS_V1_3 ? PG_STAT_STATEMENTS_COLS_V1_3 :
-1 /* fail if you forget to update this assert */ ));
tuplestore_putvalues(tupstore, tupdesc, values, nulls);
@ -2899,3 +2965,20 @@ comp_location(const void *a, const void *b)
else
return 0;
}
/*
* fast sqrt algorithm: reference from Fast inverse square root algorithms.
*/
static inline double
sqrtd(const double x)
{
double x_half = 0.5 * x;
long long int tmp = 0x5FE6EB50C7B537AAl - ( *(long long int*)&x >> 1);
double x_result = * (double*)&tmp;
x_result *= (1.5 - (x_half * x_result * x_result));
/* If retry this calculation, it becomes higher precision at sqrt */
x_result *= (1.5 - (x_half * x_result * x_result));
return x_result * x;
}