[Enhancement] Dump a new snapshot if persistent index keep too many W…

…AL (#22140)

Persistent Index for the primary key table will append wal log into `L0` index file if the following conditions are met:
1. The memory usage of `L0` is less than 10%  of `L1` usage
3. The memory usage of `L0` is greater than max snapshot size(default is 16MB)

So the `L0` index file may keep growing, and keep appending WAL. And this PR(#12862) triggers flush or merge compaction if the `L0` file size is greater than 200MB to avoid the growth of `L0` index file.

However, if the file size of `L1` is very large(e.g. 4GB) and the `L0` memory usage is less than  `L1` 10% usage but greater than 200MB(e.g. 256MB), we will always flush a new snapshot(about 256MB) even if we only update one record which causes a lot of disk IO.

So this pr change the check and dump a new snapshot if the `L0` index file keep too many wal logs.

(cherry picked from commit 817aa23)

be/src/storage/persistent_index.cpp

@@ -2753,7 +2753,7 @@ Status PersistentIndex::commit(PersistentIndexMetaPB* index_meta) {
             RETURN_IF_ERROR(_flush_l0());
         }
     }
-    _dump_snapshot |= !_flushed && _l0->file_size() > config::l0_max_file_size;
+    _dump_snapshot |= !_flushed && _l0->file_size() - _l0->memory_usage() > config::l0_max_file_size;
     // for case1 and case2
     if (_flushed) {
         // update PersistentIndexMetaPB