Change ps_status.c to explicitly track the current logical length of ps_buffer.

This saves cycles in get_ps_display() on many popular platforms, and more
importantly ensures that get_ps_display() will correctly return an empty
string if init_ps_display() hasn't been called yet.  Per trouble report
from Ray Stell, in which log_line_prefix %i produced junk early in backend
startup.

Back-patch to 8.0.  7.4 doesn't have %i and its version of get_ps_display()
makes no pretense of avoiding pad junk anyhow.

diff --git a/src/backend/utils/misc/ps_status.c b/src/backend/utils/misc/ps_status.c
index 4354adbeb4467e8949412a4a13b56dc7158ffebb..3c47c369b40b36c9081c1acbc151ee9cce61b4e4 100644 (file)
--- a/src/backend/utils/misc/ps_status.c
+++ b/src/backend/utils/misc/ps_status.c
@@ -5,7 +5,7 @@
  * to contain some useful information. Mechanism differs wildly across
  * platforms.
  *
- * $PostgreSQL: pgsql/src/backend/utils/misc/ps_status.c,v 1.33.2.1 2008/01/31 09:21:22 mha Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/misc/ps_status.c,v 1.33.2.2 2010/05/27 19:19:58 tgl Exp $
  *
  * Copyright (c) 2000-2006, PostgreSQL Global Development Group
  * various details abducted from various places
@@ -51,7 +51,7 @@ bool      update_process_title = true;
  *    (some other BSD systems)
  * PS_USE_CLOBBER_ARGV
  *    write over the argv and environment area
- *    (most SysV-like systems)
+ *    (Linux and most SysV-like systems)
  * PS_USE_WIN32
  *    push the string out as the name of a Windows event
  * PS_USE_NONE
@@ -84,15 +84,18 @@ bool        update_process_title = true;
 
 
 #ifndef PS_USE_CLOBBER_ARGV
-/* all but one options need a buffer to write their ps line in */
+/* all but one option need a buffer to write their ps line in */
 #define PS_BUFFER_SIZE 256
 static char ps_buffer[PS_BUFFER_SIZE];
 static const size_t ps_buffer_size = PS_BUFFER_SIZE;
 #else                          /* PS_USE_CLOBBER_ARGV */
 static char *ps_buffer;            /* will point to argv area */
 static size_t ps_buffer_size;  /* space determined at run time */
+static size_t last_status_len; /* use to minimize length of clobber */
 #endif   /* PS_USE_CLOBBER_ARGV */
 
+static size_t ps_buffer_cur_len;       /* nominal strlen(ps_buffer) */
+
 static size_t ps_buffer_fixed_size;        /* size of the constant prefix */
 
 /* save the original argv[] location here */
@@ -153,7 +156,7 @@ save_ps_display_args(int argc, char **argv)
        }
 
        ps_buffer = argv[0];
-       ps_buffer_size = end_of_area - argv[0];
+       last_status_len = ps_buffer_size = end_of_area - argv[0];
 
        /*
         * move the environment out of the way
@@ -225,6 +228,7 @@ init_ps_display(const char *username, const char *dbname,
    /* no ps display if you didn't call save_ps_display_args() */
    if (!save_argv)
        return;
+
 #ifdef PS_USE_CLOBBER_ARGV
    /* If ps_buffer is a pointer, it might still be null */
    if (!ps_buffer)
@@ -269,7 +273,7 @@ init_ps_display(const char *username, const char *dbname,
             username, dbname, host_info);
 #endif
 
-   ps_buffer_fixed_size = strlen(ps_buffer);
+   ps_buffer_cur_len = ps_buffer_fixed_size = strlen(ps_buffer);
 
    set_ps_display(initial_str, true);
 #endif   /* not PS_USE_NONE */
@@ -284,11 +288,11 @@ init_ps_display(const char *username, const char *dbname,
 void
 set_ps_display(const char *activity, bool force)
 {
-
+#ifndef PS_USE_NONE
+   /* update_process_title=off disables updates, unless force = true */
    if (!force && !update_process_title)
        return;
 
-#ifndef PS_USE_NONE
    /* no ps display for stand-alone backend */
    if (!IsUnderPostmaster)
        return;
@@ -302,6 +306,7 @@ set_ps_display(const char *activity, bool force)
    /* Update ps_buffer to contain both fixed part and activity */
    strlcpy(ps_buffer + ps_buffer_fixed_size, activity,
            ps_buffer_size - ps_buffer_fixed_size);
+   ps_buffer_cur_len = strlen(ps_buffer);
 
    /* Transmit new setting to kernel, if necessary */
 
@@ -314,7 +319,7 @@ set_ps_display(const char *activity, bool force)
        union pstun pst;
 
        pst.pst_command = ps_buffer;
-       pstat(PSTAT_SETCMD, pst, strlen(ps_buffer), 0, 0);
+       pstat(PSTAT_SETCMD, pst, ps_buffer_cur_len, 0, 0);
    }
 #endif   /* PS_USE_PSTAT */
 
@@ -324,13 +329,11 @@ set_ps_display(const char *activity, bool force)
 #endif   /* PS_USE_PS_STRINGS */
 
 #ifdef PS_USE_CLOBBER_ARGV
-   {
-       int         buflen;
-
-       /* pad unused memory */
-       buflen = strlen(ps_buffer);
-       MemSet(ps_buffer + buflen, PS_PADDING, ps_buffer_size - buflen);
-   }
+   /* pad unused memory; need only clobber remainder of old status string */
+   if (last_status_len > ps_buffer_cur_len)
+       MemSet(ps_buffer + ps_buffer_cur_len, PS_PADDING,
+              last_status_len - ps_buffer_cur_len);
+   last_status_len = ps_buffer_cur_len;
 #endif   /* PS_USE_CLOBBER_ARGV */
 
 #ifdef PS_USE_WIN32
@@ -365,24 +368,15 @@ const char *
 get_ps_display(int *displen)
 {
 #ifdef PS_USE_CLOBBER_ARGV
-   size_t      offset;
-
    /* If ps_buffer is a pointer, it might still be null */
    if (!ps_buffer)
    {
        *displen = 0;
        return "";
    }
-
-   /* Remove any trailing spaces to offset the effect of PS_PADDING */
-   offset = ps_buffer_size;
-   while (offset > ps_buffer_fixed_size && ps_buffer[offset - 1] == PS_PADDING)
-       offset--;
-
-   *displen = offset - ps_buffer_fixed_size;
-#else
-   *displen = strlen(ps_buffer + ps_buffer_fixed_size);
 #endif
 
+   *displen = (int) (ps_buffer_cur_len - ps_buffer_fixed_size);
+
    return ps_buffer + ps_buffer_fixed_size;
 }