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 */
 }