MDEV-34850: Busy work while parsing FILE_ records

In mariadb-backup --backup, we only have to invoke the undo_space_trunc
and log_file_op callbacks as well as validate the mini-transaction
checksums. There is absolutely no need to access recv_sys.pages or
recv_spaces. This is what the new mode recv_sys_t::store::BACKUP will do.

In the skip_the_rest: loop, the minimum that needs to be done is to
process all FILE_ records until the end of the log is reached.
Additionally, in case we invoked file_name_t::add_freed_page() for a
FREE_PAGE record before switching to the skip_the_rest: loop, we must
invoke file_name_t::remove_freed_page() for any INIT_PAGE record.
Any other records that we encounter during this parsing can be ignored;
they will eventually be processed on a subsequent call to recv_scan_log()
with store=true.

This was measured to reduce the CPU time between the messages
"InnoDB: Multi-batch recovery needed at LSN" and
"InnoDB: End of log at LSN"
by some 20%.

recv_sys_t::store: A ternary enumeration that specifies how records
should be stored: NO, BACKUP, or YES.

recv_sys_t::parse(), recv_sys_t::parse_mtr(), recv_sys_t::parse_pmem():
Replace template<bool store> with template<store storing>.

store_freed_or_init_rec(): Simplify some logic. We can look up also
the system tablespace.

extra/mariabackup/xtrabackup.cc

@@ -3405,7 +3405,8 @@ static bool xtrabackup_copy_mmap_logfile()
     recv_sys_t::parse_mtr_result r;
     const byte *start= &log_sys.buf[recv_sys.offset];
 
-    if (recv_sys.parse_mmap<false>(false) == recv_sys_t::OK)
+    if (recv_sys.parse_mmap<recv_sys_t::store::BACKUP>(false) ==
+        recv_sys_t::OK)
     {
       const byte *end;
 
@@ -3425,7 +3426,8 @@ static bool xtrabackup_copy_mmap_logfile()
           start = seq + 1;
         }
       }
-      while ((r= recv_sys.parse_mmap<false>(false)) == recv_sys_t::OK);
+      while ((r= recv_sys.parse_mmap<recv_sys_t::store::BACKUP>(false)) ==
+             recv_sys_t::OK);
 
       end= &log_sys.buf[recv_sys.offset];
 
@@ -3530,7 +3532,8 @@ static bool xtrabackup_copy_logfile()
       if (log_sys.buf[recv_sys.offset] <= 1)
         break;
 
-      if (recv_sys.parse_mtr<false>(false) == recv_sys_t::OK)
+      if (recv_sys.parse_mtr<recv_sys_t::store::BACKUP>(false) ==
+          recv_sys_t::OK)
       {
         do
         {
@@ -3540,7 +3543,8 @@ static bool xtrabackup_copy_logfile()
                                                  sequence_offset));
           *seq= 1;
         }
-        while ((r= recv_sys.parse_mtr<false>(false)) == recv_sys_t::OK);
+        while ((r= recv_sys.parse_mtr<recv_sys_t::store::BACKUP>(false)) ==
+               recv_sys_t::OK);
 
         if (ds_write(dst_log_file, log_sys.buf + start_offset,
                      recv_sys.offset - start_offset))

storage/innobase/include/log0recv.h

@@ -390,12 +390,15 @@ struct recv_sys_t
     GOT_OOM
   };
 
+  /** Whether to store parsed log records */
+  enum store{NO,BACKUP,YES};
+
 private:
   /** Parse and register one log_t::FORMAT_10_8 mini-transaction.
-  @tparam store     whether to store the records
+  @tparam storing   whether to store the records
   @param  l         log data source
   @param  if_exists if store: whether to check if the tablespace exists */
-  template<typename source,bool store>
+  template<typename source,store storing>
   inline parse_mtr_result parse(source &l, bool if_exists) noexcept;
 
   /** Rewind a mini-transaction when parse() runs out of memory.
@@ -409,20 +412,20 @@ struct recv_sys_t
 public:
   /** Parse and register one log_t::FORMAT_10_8 mini-transaction,
   without handling any log_sys.is_mmap() buffer wrap-around.
-  @tparam store     whether to store the records
-  @param  if_exists if store: whether to check if the tablespace exists */
-  template<bool store>
+  @tparam storing   whether to store the records
+  @param  if_exists storing=YES: whether to check if the tablespace exists */
+  template<store storing>
   static parse_mtr_result parse_mtr(bool if_exists) noexcept;
   /** Parse and register one log_t::FORMAT_10_8 mini-transaction,
   handling log_sys.is_mmap() buffer wrap-around.
-  @tparam store     whether to store the records
-  @param  if_exists if store: whether to check if the tablespace exists */
-  template<bool store>
+  @tparam storing   whether to store the records
+  @param  if_exists storing=YES: whether to check if the tablespace exists */
+  template<store storing>
   static parse_mtr_result parse_mmap(bool if_exists) noexcept
 #ifdef HAVE_INNODB_MMAP
     ;
 #else
-  { return parse_mtr<store>(if_exists); }
+  { return parse_mtr<storing>(if_exists); }
 #endif
 
   /** Erase log records for a page. */