To avoid showing too many memtracker on BE web pages.
The MemTracker level now has 3 levels: OVERVIEW, TASK and VERBOSE.
OVERVIEW Mainly used for main memory consumption module such as Query/Load/Metadata.
TASK is mainly used to record the memory overhead of a single task such as a single query, load, and compaction task.
VERBOSE is used for other more detailed memtrackers.
* [Enhance] Make MemTracker more accurate (#5515)
This PR main about:
1. Improve the readability of MemTrackers' name
2. Add the MemTracker of:
* Load
* Compaction
* SchemaChange
* StoragePageCache
* TabletManager
3. Change SchemaChange to a Singleon
* revise some code for Code Review
* change the name of mem_tracker
* keep reader_context have the same lifetime of rowset_reader in schema change.
* change vlog notice to log(warning) in schema change
#4995
**Implementation of Separated Page Cache**
- Add config "index_page_cache_ratio" to set the ratio of capacity of index page cache
- Change the member of StoragePageCache to maintain two type of cache
- Change the interface of StoragePageCache for selecting type of cache
- Change the usage of page cache in read_and_decompress_page in page_io.cpp
- add page type as argument
- check if current page type is available in StoragePageCache (cover the situation of ratio == 0 or 1)
- Add type as argument in superior call of read_and_decompress_page
- Change Unit Test
We create some objects which are only used for unit tests, it's not necessary,
and it may cause create duplicate instances for some classes.
This patch remove unnecessary instance of class BlockManager and StoragePageCache.
