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Injection points SMGR v17 #914

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Injection points changes
a-masterov Mar 10, 2026
f82ba63
Merge branch 'REL_17_STABLE_neon' into amasterov/injpoint-pgxn-17
a-masterov Mar 19, 2026
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53 changes: 53 additions & 0 deletions src/test/modules/injection_points/injection_points.c
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@
*/

#include "postgres.h"
#include <time.h>
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@mmeent-databricks mmeent-databricks Mar 20, 2026

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What's this used for?


#include "fmgr.h"
#include "miscadmin.h"
Expand Down Expand Up @@ -59,6 +60,8 @@ typedef struct InjectionPointCondition

/* ID of the process where the injection point is allowed to run */
int pid;
/* probability in [0,1], 1.0 = always */
double prob;
} InjectionPointCondition;

/*
Expand Down Expand Up @@ -88,13 +91,16 @@ static InjectionPointSharedState *inj_state = NULL;

extern PGDLLEXPORT void injection_error(const char *name,
const void *private_data);
extern PGDLLEXPORT void injection_error_prob(const char *name,
const void *private_data);
extern PGDLLEXPORT void injection_notice(const char *name,
const void *private_data);
extern PGDLLEXPORT void injection_wait(const char *name,
const void *private_data);

/* track if injection points attached in this process are linked to it */
static bool injection_point_local = false;
static double action2prob(const char *action, int pos);

/*
* Callback for shared memory area initialization.
Expand Down Expand Up @@ -185,6 +191,21 @@ injection_error(const char *name, const void *private_data)
elog(ERROR, "error triggered for injection point %s", name);
}

void
injection_error_prob(const char *name, const void *private_data)
{
InjectionPointCondition *condition = (InjectionPointCondition *) private_data;

if (!injection_point_allowed(condition))
return;

/* Use the probability stored in the condition. */
if ((double) rand() / (double) RAND_MAX > condition->prob)
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@mmeent-databricks mmeent-databricks Mar 20, 2026

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Why not store condition->prob as fraction of RAND_MAX?

That way, we wouldn't have to do expensive double division and compare operations every time this injection point is hit.

So, condition->prob would equal probability * RAND_MAX, which cancels out with the / (double) RAND_MAX used here, and allows us to directly compare rand() > condition->prob

return;

elog(ERROR, "error triggered for injection point %s", name);
}

void
injection_notice(const char *name, const void *private_data)
{
Expand Down Expand Up @@ -278,6 +299,11 @@ injection_points_attach(PG_FUNCTION_ARGS)
function = "injection_notice";
else if (strcmp(action, "wait") == 0)
function = "injection_wait";
else if (strncmp(action, "error-prob-", 11) == 0)
{
condition.prob = action2prob(action, 11);
function = "injection_error_prob";
}
Comment on lines +302 to +306
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@mmeent-databricks mmeent-databricks Mar 20, 2026

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why error-prob-n-nnnnn and not a suffix that's accepted by strtod? It would simplify action2prob significantly, as it wouldn't need the local copy.

Additionally, couldn't we just pass a pointer to the expected numeric suffix of the action (action + 11, or &action[11])?

else
elog(ERROR, "incorrect action \"%s\" for injection point creation", action);

Expand Down Expand Up @@ -402,3 +428,30 @@ injection_points_detach(PG_FUNCTION_ARGS)

PG_RETURN_VOID();
}

/*
* Coverts the action name into probability
*/
static double action2prob(const char *action, const int pos)
{
/*
* Simple parser: convert "0-01" -> "0.01" then strtod().
*/
const char *p = action + pos; /* points to "0-01" */
double prob;
char *endptr;
char buf[32];
int i,
j;

for (i = 0, j = 0; p[i] != '\0' && j < (int) sizeof(buf) - 1; i++)
{
buf[j++] = (p[i] == '-') ? '.' : p[i];
}
buf[j] = '\0';
errno = 0;
prob = strtod(buf, &endptr);
if (errno != 0 || endptr == buf || prob < 0.0 || prob > 1.0)
elog(ERROR, "invalid probability in action \"%s\"", action);
return prob;
}
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