Relax the requirement that all lwlocks be stored in a single array.

This makes it possible to store lwlocks as part of some other data
structure in the main shared memory segment, or in a dynamic shared
memory segment.  There is still a main LWLock array and this patch does
not move anything out of it, but it provides necessary infrastructure
for doing that in the future.

This change is likely to increase the size of LWLockPadded on some
platforms, especially 32-bit platforms where it was previously only
16 bytes.

Patch by me.  Review by Andres Freund and KaiGai Kohei.

1 files changed, 23 insertions, 21 deletions

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 4ec6981ab82..82eaf89a6b6 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -2212,49 +2212,55 @@ SELECT pg_stat_get_backend_pid(s.backendid) AS pid,
     </row>
     <row>
      <entry>lwlock-acquire</entry>
-     <entry>(LWLockId, LWLockMode)</entry>
+     <entry>(char *, int, LWLockMode)</entry>
      <entry>Probe that fires when an LWLock has been acquired.
-      arg0 is the LWLock's ID.
-      arg1 is the requested lock mode, either exclusive or shared.</entry>
+      arg0 is the LWLock's tranche.
+      arg1 is the LWLock's offset within its trance.
+      arg2 is the requested lock mode, either exclusive or shared.</entry>
     </row>
     <row>
      <entry>lwlock-release</entry>
-     <entry>(LWLockId)</entry>
+     <entry>(char *, int)</entry>
      <entry>Probe that fires when an LWLock has been released (but note
       that any released waiters have not yet been awakened).
-      arg0 is the LWLock's ID.</entry>
+      arg0 is the LWLock's tranche.
+      arg1 is the LWLock's offset within its trance.</entry>
     </row>
     <row>
      <entry>lwlock-wait-start</entry>
-     <entry>(LWLockId, LWLockMode)</entry>
+     <entry>(char *, int, LWLockMode)</entry>
      <entry>Probe that fires when an LWLock was not immediately available and
       a server process has begun to wait for the lock to become available.
-      arg0 is the LWLock's ID.
-      arg1 is the requested lock mode, either exclusive or shared.</entry>
+      arg0 is the LWLock's tranche.
+      arg1 is the LWLock's offset within its trance.
+      arg2 is the requested lock mode, either exclusive or shared.</entry>
     </row>
     <row>
      <entry>lwlock-wait-done</entry>
-     <entry>(LWLockId, LWLockMode)</entry>
+     <entry>(char *, int, LWLockMode)</entry>
      <entry>Probe that fires when a server process has been released from its
       wait for an LWLock (it does not actually have the lock yet).
-      arg0 is the LWLock's ID.
-      arg1 is the requested lock mode, either exclusive or shared.</entry>
+      arg0 is the LWLock's tranche.
+      arg1 is the LWLock's offset within its trance.
+      arg2 is the requested lock mode, either exclusive or shared.</entry>
     </row>
     <row>
      <entry>lwlock-condacquire</entry>
-     <entry>(LWLockId, LWLockMode)</entry>
+     <entry>(char *, int, LWLockMode)</entry>
      <entry>Probe that fires when an LWLock was successfully acquired when the
       caller specified no waiting.
-      arg0 is the LWLock's ID.
-      arg1 is the requested lock mode, either exclusive or shared.</entry>
+      arg0 is the LWLock's tranche.
+      arg1 is the LWLock's offset within its trance.
+      arg2 is the requested lock mode, either exclusive or shared.</entry>
     </row>
     <row>
      <entry>lwlock-condacquire-fail</entry>
-     <entry>(LWLockId, LWLockMode)</entry>
+     <entry>(char *, int, LWLockMode)</entry>
      <entry>Probe that fires when an LWLock was not successfully acquired when
       the caller specified no waiting.
-      arg0 is the LWLock's ID.
-      arg1 is the requested lock mode, either exclusive or shared.</entry>
+      arg0 is the LWLock's tranche.
+      arg1 is the LWLock's offset within its trance.
+      arg2 is the requested lock mode, either exclusive or shared.</entry>
     </row>
     <row>
      <entry>lock-wait-start</entry>
@@ -2300,10 +2306,6 @@ SELECT pg_stat_get_backend_pid(s.backendid) AS pid,
      <entry>unsigned int</entry>
     </row>
     <row>
-     <entry>LWLockId</entry>
-     <entry>int</entry>
-    </row>
-    <row>
      <entry>LWLockMode</entry>
      <entry>int</entry>
     </row>