Make the comments more clear on the fact that UpdateFullPageWrites() is not

safe to call concurrently from multiple processes.

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 49d4b36652653badad0b428474128b9bce250d64..c23cf635395ee9100c9c9f9766e3b49851cd459e 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -8442,6 +8442,9 @@ XLogReportParameters(void)
 /*
  * Update full_page_writes in shared memory, and write an
  * XLOG_FPW_CHANGE record if necessary.
+ *
+ * Note: this function assumes there is no other process running
+ * concurrently that could update it.
  */
 void
 UpdateFullPageWrites(void)
@@ -8452,8 +8455,8 @@ UpdateFullPageWrites(void)
         * Do nothing if full_page_writes has not been changed.
         *
         * It's safe to check the shared full_page_writes without the lock,
-        * because we can guarantee that there is no concurrently running
-        * process which can update it.
+        * because we assume that there is no concurrently running process
+        * which can update it.
         */
        if (fullPageWrites == Insert->fullPageWrites)
                return;
@@ -8490,7 +8493,6 @@ UpdateFullPageWrites(void)
                XLogInsert(RM_XLOG_ID, XLOG_FPW_CHANGE, &rdata);
        }
 
-
        if (!fullPageWrites)
        {
                LWLockAcquire(WALInsertLock, LW_EXCLUSIVE);