3 files changed, 21 insertions, 5 deletions
diff --git a/src/include/libpq/pqcomm.h b/src/include/libpq/pqcomm.h
index 0aceb7147c7..d11069cf8dc 100644
--- a/src/include/libpq/pqcomm.h
+++ b/src/include/libpq/pqcomm.h
@@ -128,7 +128,12 @@ typedef uint32 AuthRequest;
  *
  * The cancel request code must not match any protocol version number
  * we're ever likely to use.  This random choice should do.
+ *
+ * Before PostgreSQL v18 and the protocol version bump from 3.0 to 3.2, the
+ * cancel key was always 4 bytes.  With protocol version 3.2, it's variable
+ * length.
  */
+
 #define CANCEL_REQUEST_CODE PG_PROTOCOL(1234,5678)
 
 typedef struct CancelRequestPacket
@@ -136,7 +141,8 @@ typedef struct CancelRequestPacket
 	/* Note that each field is stored in network byte order! */
 	MsgType		cancelRequestCode;	/* code to identify a cancel request */
 	uint32		backendPID;		/* PID of client's backend */
-	uint32		cancelAuthCode; /* secret key to authorize cancel */
+	char		cancelAuthCode[FLEXIBLE_ARRAY_MEMBER];	/* secret key to
+														 * authorize cancel */
 } CancelRequestPacket;
 
 /* Application-Layer Protocol Negotiation is required for direct connections
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 603d0424354..0d8528b2875 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -191,8 +191,8 @@ extern PGDLLIMPORT pg_time_t MyStartTime;
 extern PGDLLIMPORT TimestampTz MyStartTimestamp;
 extern PGDLLIMPORT struct Port *MyProcPort;
 extern PGDLLIMPORT struct Latch *MyLatch;
-extern PGDLLIMPORT bool MyCancelKeyValid;
-extern PGDLLIMPORT int32 MyCancelKey;
+extern PGDLLIMPORT char MyCancelKey[];
+extern PGDLLIMPORT uint8 MyCancelKeyLength;
 extern PGDLLIMPORT int MyPMChildSlot;
 
 extern PGDLLIMPORT char OutputFileName[];
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 022fd8ed933..016dfd9b3f6 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -57,15 +57,25 @@ typedef enum
 } ProcSignalBarrierType;
 
 /*
+ * Length of query cancel keys generated.
+ *
+ * Note that the protocol allows for longer keys, or shorter, but this is the
+ * length we actually generate.  Client code, and the server code that handles
+ * incoming cancellation packets from clients, mustn't use this hardcoded
+ * length.
+ */
+#define MAX_CANCEL_KEY_LENGTH  32
+
+/*
  * prototypes for functions in procsignal.c
  */
 extern Size ProcSignalShmemSize(void);
 extern void ProcSignalShmemInit(void);
 
-extern void ProcSignalInit(bool cancel_key_valid, int32 cancel_key);
+extern void ProcSignalInit(char *cancel_key, int cancel_key_len);
 extern int	SendProcSignal(pid_t pid, ProcSignalReason reason,
 						   ProcNumber procNumber);
-extern void SendCancelRequest(int backendPID, int32 cancelAuthCode);
+extern void SendCancelRequest(int backendPID, char *cancel_key, int cancel_key_len);
 
 extern uint64 EmitProcSignalBarrier(ProcSignalBarrierType type);
 extern void WaitForProcSignalBarrier(uint64 generation);