Add get_pin_limit_hook

Author: knizhnik

src/backend/storage/buffer/bufmgr.c

@@ -68,6 +68,7 @@
 #include "utils/resowner.h"
 #include "utils/timestamp.h"
 
+uint32 (*get_pin_limit_hook)(void);
 
 /* Note: these two macros only work on shared buffers, not local ones! */
 #define BufHdrGetBlock(bufHdr)	((Block) (BufferBlocks + ((Size) (bufHdr)->buf_id) * BLCKSZ))
@@ -2526,7 +2527,7 @@ GetVictimBuffer(BufferAccessStrategy strategy, IOContext io_context)
 uint32
 GetPinLimit(void)
 {
-	return MaxProportionalPins;
+	return get_pin_limit_hook ? get_pin_limit_hook() : MaxProportionalPins;
 }
 
 /*

src/include/storage/bufmgr.h

@@ -334,6 +334,7 @@ extern int	GetAccessStrategyPinLimit(BufferAccessStrategy strategy);
 
 extern void FreeAccessStrategy(BufferAccessStrategy strategy);
 
+extern uint32 (*get_pin_limit_hook)(void);
 
 /* inline functions */