MDB_READERS_FULL: Environment maxreaders limit reached 
From here:
https://github.com/moneroexamples/openmonero/issues/121#issuecomment-456610170

```
2019-01-23 05:59:21.882     7fd86ffd7700        WARNING blockchain.db.lmdb      src/blockchain_db/lmdb/db_lmdb.cpp:73Failed to create a read transaction for the db: MDB_READERS_FULL: Environment maxreaders limit reached               
2019-01-23 05:59:21,886 [I,OM,TxSearch.cpp:virtual void xmreg::TxSearch::operator()():139] A1zPXK: analyzing 200 blocks from 31800 to 31999 out of 1129675 blocks                                                                         
2019-01-23 05:59:21,918 [I,OM,TxSearch.cpp:virtual void xmreg::TxSearch::operator()():139] 9tE2Xc: analyzing 200 blocks from 155000 to 155199 out of 1129675 blocks                                                                       
2019-01-23 05:59:21,947 [E,OM,TxSearch.cpp:virtual void xmreg::TxSearch::operator()():605] 9sfsS3: exception in TxSearch!    
```
Happens at about 120 TxSearch threads. 

This will also stop monero daemon:

```
status
2019-01-23 06:37:44.000     7fc006d0c700        WARNING blockchain.db.lmdb      src/blockchain_db/lmdb/db_lmdb.cpp:73Failed to create a read transaction for the db: MDB_READERS_FULL: Environment maxreaders limit reached               
2019-01-23 06:37:44.005     7fc006d0c700        ERROR   default contrib/epee/include/console_handler.h:392      Exception at [console_handler], what=Failed to create a read transaction for the db: MDB_READERS_FULL: Environment maxreaders limit reached
```

Before discussed in monero here: https://github.com/monero-project/monero/issues/2741