[#19134] YSQL, ASH: Setting ASH circular buffer size based on the num…

…ber of cores

Summary:
The default value of the guc/gflag yb_ash_circular_buffer_size is changed to zero.

If the user doesn't specify the value of guc/gflag, this is overridden based on the
number of cores available on the machine. If the user specifies the value, then
the circular buffer is created with the size the user provides.

The defaults are -
- 32 MiB for 1-2 cores
- 64 MiB for 3-4 cores
- 128 MiB for 5-8 cores
- 256 MiB for 9-16 cores
- 512 MiB for 17-32 cores
- 1024 MiB for > 32 cores
Jira: DB-7932

Test Plan:
Manually tested

In mac
```
$ sysctl -n hw.ncpu
10

$ bin/yb-ctl start --tserver_flags='"allowed_preview_flags_csv=ysql_yb_enable_ash,ysql_yb_ash_enable_infra",ysql_yb_ash_enable_infra=true,ysql_yb_enable_ash=true'

yugabyte=# show yb_ash_circular_buffer_size;
 yb_ash_circular_buffer_size
-----------------------------
 256MB

$ bin/yb-ctl restart --tserver_flags='"allowed_preview_flags_csv=ysql_yb_enable_ash,ysql_yb_ash_enable_infra",ysql_yb_ash_enable_infra=true,ysql_yb_enable_ash=true,ysql_yb_ash_circular_buffer_size=10240'

yugabyte=# show yb_ash_circular_buffer_size;
 yb_ash_circular_buffer_size
-----------------------------
 10MB
```

In alma linux 8

```
$ nproc
4

$ bin/yb-ctl start --tserver_flags='"allowed_preview_flags_csv=ysql_yb_enable_ash,ysql_yb_ash_enable_infra",ysql_yb_ash_enable_infra=true,ysql_yb_enable_ash=true'

yugabyte=# show yb_ash_circular_buffer_size;
 yb_ash_circular_buffer_size
-----------------------------
 64MB

$ bin/yb-ctl restart --tserver_flags='"allowed_preview_flags_csv=ysql_yb_enable_ash,ysql_yb_ash_enable_infra",ysql_yb_ash_enable_infra=true,ysql_yb_enable_ash=true,ysql_yb_ash_circular_buffer_size=10240'

yugabyte=# show yb_ash_circular_buffer_size;
 yb_ash_circular_buffer_size
-----------------------------
 10MB
```

Reviewers: jason, amitanand, hbhanawat

Reviewed By: jason

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D37713

src/postgres/src/backend/utils/misc/guc.c

@@ -4158,12 +4158,12 @@ static struct config_int ConfigureNamesInt[] =
 	{
 		{"yb_ash_circular_buffer_size", PGC_POSTMASTER, STATS_MONITORING,
 			gettext_noop("Size (in KiBs) of ASH circular buffer that stores the samples"),
-			NULL,
+			gettext_noop("If this is 0, the size will be calculated based on the number of cores"),
 			GUC_UNIT_KB
 		},
 		&yb_ash_circular_buffer_size,
-		16 * 1024, 1, INT_MAX,
-		NULL, NULL, NULL
+		0, 0, INT_MAX,
+		yb_ash_circular_buffer_size_check_hook, NULL, NULL
 	},
 
 	{

src/postgres/src/backend/utils/misc/yb_ash.c

@@ -163,6 +163,16 @@ yb_enable_ash_check_hook(bool *newval, void **extra, GucSource source)
 	return true;
 }
 
+bool
+yb_ash_circular_buffer_size_check_hook(int *newval, void **extra, GucSource source)
+{
+	/* Autocompute yb_ash_circular_buffer_size if zero */
+	if (*newval == 0)
+		*newval = YBCGetCircularBufferSizeInKiBs();
+
+	return true;
+}
+
 void
 YbAshRegister(void)
 {
@@ -219,6 +229,7 @@ YbAshSetDatabaseId(Oid database_id)
 static int
 yb_ash_cb_max_entries(void)
 {
+	Assert(yb_ash_circular_buffer_size != 0);
 	return yb_ash_circular_buffer_size * 1024 / sizeof(YBCAshSample);
 }
 
@@ -687,9 +698,10 @@ yb_ash_sighup(SIGNAL_ARGS)
 void
 YbAshMain(Datum main_arg)
 {
+	Assert(yb_ash_circular_buffer_size != 0);
 	ereport(LOG,
-			(errmsg("starting bgworker yb_ash collector with max buffer entries %d",
-					yb_ash->max_entries)));
+			(errmsg("starting bgworker yb_ash collector with circular buffer size %d bytes",
+					yb_ash_circular_buffer_size * 1024)));
 
 	/* Register functions for SIGTERM/SIGHUP management */
 	pqsignal(SIGHUP, yb_ash_sighup);

src/postgres/src/include/yb_ash.h

@@ -64,6 +64,9 @@ extern void YbAshFillSampleWeight(int samples_considered);
 extern bool yb_enable_ash_check_hook(bool *newval,
 									 void **extra,
 									 GucSource source);
+extern bool yb_ash_circular_buffer_size_check_hook(int *newval,
+												   void **extra,
+												   GucSource source);
 
 extern void YbAshSetMetadata(void);
 extern void YbAshUnsetMetadata(void);

src/yb/ash/wait_state.cc

@@ -16,6 +16,7 @@
 #include <arpa/inet.h>
 
 #include "yb/util/debug-util.h"
+#include "yb/util/size_literals.h"
 #include "yb/util/tostring.h"
 #include "yb/util/trace.h"
 
@@ -53,7 +54,7 @@ DEFINE_RUNTIME_PG_PREVIEW_FLAG(bool, yb_enable_ash, false,
     "and various background activities. This does nothing if "
     "ysql_yb_enable_ash_infra is disabled.");
 
-DEFINE_NON_RUNTIME_PG_FLAG(int32, yb_ash_circular_buffer_size, 16 * 1024,
+DEFINE_NON_RUNTIME_PG_FLAG(int32, yb_ash_circular_buffer_size, 0,
     "Size (in KiBs) of ASH circular buffer that stores the samples");
 
 DEFINE_RUNTIME_PG_FLAG(int32, yb_ash_sampling_interval_ms, 1000,
@@ -384,6 +385,25 @@ std::vector<WaitStatesDescription> WaitStateInfo::GetWaitStatesDescription() {
   return desc;
 }
 
+int WaitStateInfo::GetCircularBufferSizeInKiBs() {
+  int num_cpus = base::NumCPUs();
+  int bytes;
+  if (num_cpus <= 2) {
+    bytes = 32_MB;
+  } else if (num_cpus <= 4) {
+    bytes = 64_MB;
+  } else if (num_cpus <= 8) {
+    bytes = 128_MB;
+  } else if (num_cpus <= 16) {
+    bytes = 256_MB;
+  } else if (num_cpus <= 32) {
+    bytes = 512_MB;
+  } else {
+    bytes = 1024_MB;
+  }
+  return bytes / 1024;
+}
+
 //
 // ScopedAdoptWaitState
 //

src/yb/ash/wait_state.h

@@ -431,6 +431,7 @@ class WaitStateInfo {
   bool IsConcurrentUpdatesEnabled();
 
   static std::vector<WaitStatesDescription> GetWaitStatesDescription();
+  static int GetCircularBufferSizeInKiBs();
 
  protected:
   void VTraceTo(Trace* trace, int level, GStringPiece data);

src/yb/yql/pggate/util/ybc_util.cc

@@ -506,6 +506,10 @@ YBCWaitEventDescriptor YBCGetWaitEventDescription(size_t index) {
   return { 0, nullptr };
 }
 
+int YBCGetCircularBufferSizeInKiBs() {
+  return ash::WaitStateInfo::GetCircularBufferSizeInKiBs();
+}
+
 int YBCGetCallStackFrames(void** result, int max_depth, int skip_count) {
   return google::GetStackTrace(result, max_depth, skip_count);
 }

src/yb/yql/pggate/util/ybc_util.h

@@ -348,6 +348,7 @@ const char* YBCGetWaitEventType(uint32_t wait_event_info);
 uint8_t YBCGetQueryIdForCatalogRequests();
 int YBCGetRandomUniformInt(int a, int b);
 YBCWaitEventDescriptor YBCGetWaitEventDescription(size_t index);
+int YBCGetCircularBufferSizeInKiBs();
 
 int YBCGetCallStackFrames(void** result, int max_depth, int skip_count);