leveldb write slow after database is large？

Hello, I encountered some problems when using leveldb. The scenario is like this: I kept writing key value to the database. At first, it was very fast, but after writing for an hour, I found that the writing became slower and slower. Before each write, it will query whether the key exists. The key value written is only tens of bytes, but eventually hundreds of terabytes of data will be written. Is the speed of this write affected by the size of the database?