[SPDK] Re: Rocksdb with SPDK

Hi Dimitra

> From: dimitra.giantsidi(a)gmail.com <dimitra.giantsidi(a)gmail.com>> 
> Hi all,
> 
> I am running Rocksdb on top of a blobfs filesystem and I have a couple of
> questions.
> 
> 1. What exactly does the ```sanitize_path()``` function do and why do we need to
> sanitize the path before opening a file? If the fname is /mnt/rocksdb/log, the
> sanitize path returns /log .. What does that means for my application?

Blobfs doesn't actually have a hierarchical directory structure. It stores the file names as string keys. Therefore it is very important that the same file, however it's described via valid POSIX paths, translate into a consistent string name. That's what sanitize_path() is doing.

> 2. the file->Sync() operations fails with a message "Not Implemented". In
> particular, I am having the following code :
> 
> ```
> if (!FLAGS__spdk.empty()) {
>                         FLAGS_env = rocksdb::NewSpdkEnv(FLAGS_env, FLAGS_dir,
> FLAGS__spdk, FLAGS__spdk_bdev, FLAGS__spdk_cache_size);
>                         fprintf(stdout, "Using rocksdb::NewSpdkEnv() environment.\n");
>                         if (FLAGS_env == nullptr) {
>                                 fprintf(stderr, "Could not load SPDK blobfs - check that SPDK
> mkfs was run "
>                                                 "against block device %s.\n",
> FLAGS__spdk_bdev.c_str());
>                                 exit(1);
>                         }
>                 }
> 
>                 unique_ptr<WritableFile> file;
>                 EnvOptions soptions;
> 
>                 rocksdb::Slice data = return_data(FLAGS__value_size);
>                 Status s = FLAGS_env->NewWritableFile(FLAGS_file, &file, soptions);
>                 if (!s.ok()) {
>                         fprintf(stderr, "oops ..\n");
>                         abort();
>                 }
> 
>                 size_t size = 0;
>                 size_t total_size = FLAGS_total_size*1024;
>                 struct timeval start_time, end_time;
>                 gettimeofday(&start_time, NULL);
>                 while (size < total_size) {
>                         s = file->Append(data);
> 
>                         if (s.ok()) {
>                                 s = file->Sync();
>                         }
> 
>                         size += FLAGS__value_size;
> 
>                         if (!s.ok()) {
>                                 fprintf(stdout, "written %d bytes to %s (%s)..\n", size,
> FLAGS_file.c_str(), s.ToString().c_str());
>                                 abort();
>                         }
>                 }
> ```
> 
> However, I am seeing that the rocksdb::SpdkWritableFile::Sync() is implemented

Where is that "Not implemented" message coming from in the code? Is that something from RocksDB? It does look like sync is implemented.

> ..
> Any ideas?
> Thanks for your help :)
> 
> Dimitra
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