Further effort at preventing memory map dump from affecting the results.

Rather than elog'ing immediately, push the map data into a preallocated
StringInfo.  Perhaps this will prevent some of the mid-operation
allocations that are evidently happening now.

Discussion: https://postgr.es/m/25495.1524517820@sss.pgh.pa.us

diff --git a/src/backend/port/win32_shmem.c b/src/backend/port/win32_shmem.c
index 9e42665ed62438f54c136d6c2ddddaf13e928284..dd66756b99129cad82726b8cd5c538ae01089c23 100644 (file)
--- a/src/backend/port/win32_shmem.c
+++ b/src/backend/port/win32_shmem.c
@@ -12,6 +12,7 @@
  */
 #include "postgres.h"
 
+#include "lib/stringinfo.h"
 #include "miscadmin.h"
 #include "storage/dsm.h"
 #include "storage/ipc.h"
@@ -54,13 +55,17 @@ mi_state(DWORD code)
        return "???";
 }
 
+/*
+ * Append memory dump to buf.  To avoid affecting the memory map mid-run,
+ * buf should be preallocated to be bigger than needed.
+ */
 static void
-dumpmem(const char *reason)
+dumpmem(StringInfo buf, const char *reason)
 {
        char       *addr = 0;
        MEMORY_BASIC_INFORMATION mi;
 
-       elog(LOG, "%s memory map", reason);
+       appendStringInfo(buf, "%s memory map:", reason);
        do
        {
                memset(&mi, 0, sizeof(mi));
@@ -68,12 +73,13 @@ dumpmem(const char *reason)
                {
                        if (GetLastError() == ERROR_INVALID_PARAMETER)
                                break;
-                       elog(LOG, "VirtualQuery failed: %lu", GetLastError());
+                       appendStringInfo(buf, "\nVirtualQuery failed: %lu", GetLastError());
                        break;
                }
-               elog(LOG, "0x%p+0x%p %s (alloc 0x%p) %s",
-                        mi.BaseAddress, (void *) mi.RegionSize,
-                        mi_type(mi.Type), mi.AllocationBase, mi_state(mi.State));
+               appendStringInfo(buf, "\n0x%p+0x%p %s (alloc 0x%p) %s",
+                                                mi.BaseAddress, (void *) mi.RegionSize,
+                                                mi_type(mi.Type), mi.AllocationBase,
+                                                mi_state(mi.State));
                addr += mi.RegionSize;
        } while (addr > 0);
 }
@@ -442,11 +448,16 @@ PGSharedMemoryReAttach(void)
 {
        PGShmemHeader *hdr;
        void       *origUsedShmemSegAddr = UsedShmemSegAddr;
+       StringInfoData buf;
 
        Assert(UsedShmemSegAddr != NULL);
        Assert(IsUnderPostmaster);
 
-       dumpmem("before VirtualFree");
+       /* Ensure buf is big enough that it won't grow mid-operation */
+       initStringInfo(&buf);
+       enlargeStringInfo(&buf, 128 * 1024);
+
+       dumpmem(&buf, "before VirtualFree");
 
        /*
         * Release memory region reservation that was made by the postmaster
@@ -455,20 +466,19 @@ PGSharedMemoryReAttach(void)
                elog(FATAL, "failed to release reserved memory region (addr=%p): error code %lu",
                         UsedShmemSegAddr, GetLastError());
 
-       dumpmem("after VirtualFree");
+       dumpmem(&buf, "after VirtualFree");
 
        hdr = (PGShmemHeader *) MapViewOfFileEx(UsedShmemSegID, FILE_MAP_READ | FILE_MAP_WRITE, 0, 0, 0, UsedShmemSegAddr);
        if (!hdr)
        {
                DWORD           maperr = GetLastError();
 
-               dumpmem("after failed MapViewOfFileEx");
+               dumpmem(&buf, "after failed MapViewOfFileEx");
+               elog(LOG, "%s", buf.data);
 
                elog(FATAL, "could not reattach to shared memory (key=%p, addr=%p): error code %lu",
                         UsedShmemSegID, UsedShmemSegAddr, maperr);
        }
-       else
-               dumpmem("after MapViewOfFileEx");
        if (hdr != origUsedShmemSegAddr)
                elog(FATAL, "reattaching to shared memory returned unexpected address (got %p, expected %p)",
                         hdr, origUsedShmemSegAddr);
@@ -476,6 +486,8 @@ PGSharedMemoryReAttach(void)
                elog(FATAL, "reattaching to shared memory returned non-PostgreSQL memory");
        dsm_set_control_handle(hdr->dsm_control);
 
+       pfree(buf.data);
+
        UsedShmemSegAddr = hdr;         /* probably redundant */
 }