page_parser very slow when large btree (~100GB)

[Yves Trudeau]

When there're large btrees, the fact that the page_parser creates one file per page becomes a performance bottleneck because of the filesystem. The following patch creates one file per btree and can be as much as 20x faster:

--- page_parser.c 2013-08-29 13:25:49.869474000 -0400
+++ page_parser_1_file_per_btree.c 2013-08-29 13:32:48.947581652 -0400
@@ -159,10 +159,10 @@
                 exit(-1);
                 }
             sprintf(dir_name, "%s/%lu-%lu", dir_prefix, index_id.high, index_id.low);
- if(mkdir(dir_name, 0755) && errno != EEXIST) {
- fprintf(stderr, "Can't make a directory %s: %s\n", dir_name, strerror(errno));
- exit(-1);
- }
+ //if(mkdir(dir_name, 0755) && errno != EEXIST) {
+ // fprintf(stderr, "Can't make a directory %s: %s\n", dir_name, strerror(errno));
+ // exit(-1);
+ // }
        }
     else{
             sprintf(dir_name, "pages-%u/FIL_PAGE_TYPE_BLOB", (unsigned int)timestamp);
@@ -175,7 +175,7 @@

     // Compose page file_name
     if(is_index){
- sprintf(file_name, "%s/%08lu-%08lu.page", dir_name, 0, page_id);
+ sprintf(file_name, "%s", dir_name);
         }
     else{
         sprintf(file_name, "%s/page-%08lu.page", dir_name, page_id);