ffd->txn_dir_cache

[Daniel Shahaf]

>From svn_fs_fs__initialize_txn_caches()

[[[
  /* We don't support caching for concurrent transactions in the SAME
   * FSFS session. Maybe, you forgot to clean POOL. */
  if (ffd->txn_dir_cache != NULL || ffd->concurrent_transactions)
    {
      ffd->txn_dir_cache = NULL;
      ffd->concurrent_transactions = TRUE;

      return SVN_NO_ERROR;
    }

  SVN_ERR(create_cache(&ffd->txn_dir_cache, ...));
]]]

So:

2. Presumably create_cache() should be guarded by 'if 
(!ffd->concurrent_transactions)'.

3. This writes to an int (ffd->concurrent_transactions) concurrently from
   multiple threads.  Shouldn't it be using an atomic type instead?

1. Couldn't we simplify this code by taking advantage of ID's being 
txn-specific?

   283606893804/ <_0.0.t6-7>
   283974816614/ <0-4.0.r4/0>