Save index file in postgres data dir (#256)

src/hnsw/build.c

@@ -426,9 +426,9 @@ static void BuildIndex(
     struct stat            index_file_stat;
     char                  *result_buf = NULL;
     char                  *tmp_index_file_path = NULL;
-    const char            *tmp_index_file_fmt_str = "/tmp/ldb-index-%d.bin";
-    // size of static name + max digits of uint32 (Oid) 10 + 1 for nullbyte and - 2 for %d format specifier
-    const uint32       tmp_index_file_char_cnt = strlen(tmp_index_file_fmt_str) + 9;
+    const char            *tmp_index_file_fmt_str = "%s/ldb-index-%d.bin";
+    // parent_dir + max digits of uint32 (Oid) 10
+    const uint32       tmp_index_file_char_cnt = MAXPGPATH + strlen(tmp_index_file_fmt_str) + 10;
     int                index_file_fd;
     int                munmap_ret;
     usearch_metadata_t metadata;
@@ -514,10 +514,11 @@ static void BuildIndex(
     if(buildstate->index_file_path == NULL) {
         // Save index into temporary file
         // To later mmap it into memory
-        // Filename is /tmp/ldb-index-$relfilenode.bin
         // The file will be removed in the end
         tmp_index_file_path = palloc0(tmp_index_file_char_cnt);
-        snprintf(tmp_index_file_path, tmp_index_file_char_cnt, tmp_index_file_fmt_str, index->rd_rel->relfilenode);
+        // Create index file directory string: $pg_data_dir/ldb_indexes/index-$relfilenode.bin
+        snprintf(
+            tmp_index_file_path, tmp_index_file_char_cnt, tmp_index_file_fmt_str, DataDir, index->rd_rel->relfilenode);
         usearch_save(buildstate->usearch_index, tmp_index_file_path, NULL, &error);
         assert(error == NULL);
         index_file_fd = open(tmp_index_file_path, O_RDONLY);