Re: [HACKERS] loading libraries on Postmaster startup - Mailing list pgsql-patches

Joe Conway wrote:
> Tom Lane wrote:
>> Joe Conway <mail@joeconway.com> writes:
>>> In my testing with PL/R, it reduces the first call to a PL/R function
>>> (after connecting) from almost 2 seconds, down to about 8 ms.
>>
>> Hm, pretty significant.  Can you measure any per-fork cost (ie, the loss
>> incurred by children that don't use PL/R)?  Is there any measurable
>> benefit for our other PLs (plperl etc)?
>
> Here's what I got:
>
> 10000 connect/disconnect in tight loop
> ----------------------------------------------------------
> condition        time        top
> ----------------------------------------------------------
> with no preload        87 seconds    ~10% CPU, ~2.2 MB
> with plr preload    133 seconds    ~10% CPU, ~13 MB
> with plperl preload    92 seconds    ~10% CPU, ~3.2 MB
> with pltcl preload    88 seconds    ~10% CPU, ~2.3 MB
> with plpython preload    93 seconds    ~10% CPU, ~2.3 MB
>
>
> 1000 connect/"select some_simple_func()"/disconnect in tight loop
> ------------------------------------------------------------------
> condition            time            top
> ------------------------------------------------------------------
> plr-func without preload    739 seconds    ~60% CPU, ~13 MB
> plr-func with preload        26 seconds    ~10% CPU, ~13 MB
> plperl-func without preload    46 seconds    ~4% CPU, ~3.2 MB
> plperl-func with preload    33 seconds    ~3% CPU, ~3.2 MB
> pltcl-func without preload    22 seconds    ~5% CPU, ~2.3 MB
> pltcl-func with preload        17 seconds    ~4% CPU, ~2.3 MB
> plpython-func without preload    33 seconds    ~4% CPU, ~2.3 MB
> plpython-func with preload    31 seconds    ~4% CPU, ~2.3 MB
>

Here's an updated copy of the patch. The original patch was failing due
to code drift in cvs.

Peter's suggestion (__attribute__((constructor))) is interesting, but it
appears to be a gcc specific extension, and hence non-portable.

I'd still like to see this applied if there are no other objections.
 From the above info it is apparent that the benefit outweighs the cost
for plperl and pltcl (although not as significantly as for plr).

Joe
Index: doc/src/sgml/runtime.sgml
===================================================================
RCS file: /opt/src/cvs/pgsql-server/doc/src/sgml/runtime.sgml,v
retrieving revision 1.169
diff -c -r1.169 runtime.sgml
*** doc/src/sgml/runtime.sgml    19 Feb 2003 04:06:28 -0000    1.169
--- doc/src/sgml/runtime.sgml    27 Feb 2003 18:46:39 -0000
***************
*** 1781,1786 ****
--- 1781,1815 ----
       </varlistentry>

       <varlistentry>
+       <term><varname>PRELOAD_LIBRARIES</varname> (<type>string</type>)</term>
+       <indexterm><primary>preload_libraries</></>
+       <listitem>
+        <para>
+         This variable specifies one or more shared libraries that are to be
+     preloaded at Postmaster start. An initialization function can also be
+     optionally specified by adding a colon followed by the name of the
+     initialization function after the library name. For example
+     <literal>'$libdir/mylib:init_mylib'</literal> would cause <literal>mylib</>
+     to be preloaded and <literal>init_mylib</> to be executed. If more than
+     one library is to be loaded, they must be delimited with a comma.
+        </para>
+
+        <para>
+         If <literal>mylib</> is not found, the postmaster will fail to start.
+     However, if <literal>init_mylib</> is not found, <literal>mylib</> will
+     still be preloaded without executing the initialization function.
+        </para>
+
+        <para>
+         By preloading a shared library (and initializing it if applicable),
+     the library startup time is avoided when the library is used later in a
+     specific backend. However there is a cost in terms of memory duplication
+     as every backend is forked, whether or not the library is used.
+        </para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
        <term><varname>REGEX_FLAVOR</varname> (<type>string</type>)</term>
        <indexterm><primary>regular expressions</></>
        <listitem>
Index: src/backend/postmaster/postmaster.c
===================================================================
RCS file: /opt/src/cvs/pgsql-server/src/backend/postmaster/postmaster.c,v
retrieving revision 1.307
diff -c -r1.307 postmaster.c
*** src/backend/postmaster/postmaster.c    23 Feb 2003 04:48:19 -0000    1.307
--- src/backend/postmaster/postmaster.c    27 Feb 2003 18:46:39 -0000
***************
*** 205,210 ****
--- 205,212 ----
  bool        Log_connections = false;
  bool        Db_user_namespace = false;

+ /* list of library:init-function to be preloaded */
+ char       *preload_libraries_string = NULL;

  /* Startup/shutdown state */
  static pid_t StartupPID = 0,
***************
*** 644,649 ****
--- 646,658 ----
      if (EnableSSL)
          secure_initialize();
  #endif
+
+     /*
+      * process any libraries that should be preloaded and
+      * optionally pre-initialized
+      */
+     if (preload_libraries_string)
+         process_preload_libraries(preload_libraries_string);

      /*
       * Fork away from controlling terminal, if -S specified.
Index: src/backend/utils/init/miscinit.c
===================================================================
RCS file: /opt/src/cvs/pgsql-server/src/backend/utils/init/miscinit.c,v
retrieving revision 1.100
diff -c -r1.100 miscinit.c
*** src/backend/utils/init/miscinit.c    27 Jan 2003 00:51:06 -0000    1.100
--- src/backend/utils/init/miscinit.c    27 Feb 2003 18:46:39 -0000
***************
*** 1044,1046 ****
--- 1044,1135 ----
               "which is not compatible with this version %s.",
               file_major, file_minor, version_string);
  }
+
+ /*-------------------------------------------------------------------------
+  *                Library preload support
+  *-------------------------------------------------------------------------
+  */
+
+ #if defined(__mc68000__) && defined(__ELF__)
+ typedef int32 ((*func_ptr) ());
+ #else
+ typedef char *((*func_ptr) ());
+ #endif
+
+ /*
+  * process any libraries that should be preloaded and
+  * optionally pre-initialized
+  */
+ void
+ process_preload_libraries(char *preload_libraries_string)
+ {
+     char       *rawstring;
+     List       *elemlist;
+     List       *l;
+
+     if (preload_libraries_string == NULL)
+         return;
+
+     /* Need a modifiable copy of string */
+     rawstring = pstrdup(preload_libraries_string);
+
+     /* Parse string into list of identifiers */
+     if (!SplitIdentifierString(rawstring, ',', &elemlist))
+     {
+         /* syntax error in list */
+         pfree(rawstring);
+         freeList(elemlist);
+         elog(LOG, "invalid list syntax for preload_libraries configuration option");
+     }
+
+     foreach(l, elemlist)
+     {
+         char       *tok = (char *) lfirst(l);
+         char       *sep = strstr(tok, ":");
+         char       *filename = NULL;
+         char       *funcname = NULL;
+         func_ptr    initfunc;
+
+         if (sep)
+         {
+             /*
+              * a colon separator implies there is an initialization function
+              * that we need to run in addition to loading the library
+              */
+             size_t        filename_len = sep - tok;
+             size_t        funcname_len = strlen(tok) - filename_len - 1;
+
+             filename = (char *) palloc(filename_len + 1);
+             memset(filename, '\0', filename_len + 1);
+             snprintf(filename, filename_len + 1, "%s", tok);
+
+             funcname = (char *) palloc(funcname_len + 1);
+             memset(funcname, '\0', funcname_len + 1);
+             snprintf(funcname, funcname_len + 1, "%s", sep + 1);
+         }
+         else
+         {
+             /*
+              * no separator -- just load the library
+              */
+             filename = pstrdup(tok);
+             funcname = NULL;
+         }
+
+         initfunc = (func_ptr) load_external_function(filename, funcname, false, NULL);
+         if (initfunc)
+             (*initfunc)();
+
+         elog(LOG, "preloaded library %s with initialization function %s", filename, funcname);
+
+         if (filename != NULL)
+             pfree(filename);
+
+         if (funcname != NULL)
+             pfree(funcname);
+     }
+
+     pfree(rawstring);
+     freeList(elemlist);
+ }
+
Index: src/backend/utils/misc/guc.c
===================================================================
RCS file: /opt/src/cvs/pgsql-server/src/backend/utils/misc/guc.c,v
retrieving revision 1.115
diff -c -r1.115 guc.c
*** src/backend/utils/misc/guc.c    23 Feb 2003 23:27:21 -0000    1.115
--- src/backend/utils/misc/guc.c    27 Feb 2003 18:46:39 -0000
***************
*** 60,65 ****
--- 60,66 ----
  extern bool autocommit;
  extern int    CommitDelay;
  extern int    CommitSiblings;
+ extern char *preload_libraries_string;

  #ifdef HAVE_SYSLOG
  extern char *Syslog_facility;
***************
*** 812,817 ****
--- 813,824 ----
      {
          {"lc_time", PGC_USERSET}, &locale_time,
          "C", locale_time_assign, NULL
+     },
+
+     {
+         {"preload_libraries", PGC_POSTMASTER, GUC_LIST_INPUT | GUC_LIST_QUOTE},
+         &preload_libraries_string,
+         "", NULL, NULL
      },

      {
Index: src/backend/utils/misc/postgresql.conf.sample
===================================================================
RCS file: /opt/src/cvs/pgsql-server/src/backend/utils/misc/postgresql.conf.sample,v
retrieving revision 1.70
diff -c -r1.70 postgresql.conf.sample
*** src/backend/utils/misc/postgresql.conf.sample    6 Feb 2003 20:25:33 -0000    1.70
--- src/backend/utils/misc/postgresql.conf.sample    27 Feb 2003 18:46:39 -0000
***************
*** 213,216 ****
--- 213,217 ----
  #transform_null_equals = false
  #statement_timeout = 0        # 0 is disabled, in milliseconds
  #db_user_namespace = false
+ #preload_libraries = ''

Index: src/include/miscadmin.h
===================================================================
RCS file: /opt/src/cvs/pgsql-server/src/include/miscadmin.h,v
retrieving revision 1.116
diff -c -r1.116 miscadmin.h
*** src/include/miscadmin.h    22 Feb 2003 05:57:45 -0000    1.116
--- src/include/miscadmin.h    27 Feb 2003 18:46:39 -0000
***************
*** 288,293 ****
--- 288,294 ----
                               unsigned long id2);

  extern void ValidatePgVersion(const char *path);
+ extern void process_preload_libraries(char *preload_libraries_string);

  /* these externs do not belong here... */
  extern void IgnoreSystemIndexes(bool mode);