In mow, primary key cache have a big impact on load performance, so we add a new cache type to seperate
it from page cache to make it more flexible in some cases
The core is due to a DCHECK:
F0513 22:48:56.059758 3996895 tablet.cpp:2690] Check failed: num_to_read == num_read
Finally, we found that the DCHECK failure is due to page cache:
1. At first we have 20 segments, which id is 0-19.
2. For MoW table, memtable flush process will calculate the delete bitmap. In this procedure, the index pages and data pages of PrimaryKeyIndex is loaded to cache
3. Segment compaction compact all these 10 segments to 2 segment, and rename it to id 0,1
4. Finally, before the load commit, we'll calculate delete bitmap between segments in current rowset. This procedure need to iterator primary key index of each segments, but when we access data of new compacted segments, we read data of old segments in page cache
To fix this issue, the best policy is:
1. Add a crc32 or last modified time to CacheKey.
2. Or invalid related cache keys after segment compaction.
For policy 1, we don't have crc32 in segment footer, and getting the last-modified-time needs to perform 1 additional disk IO.
For policy 2, we need to add additional page cache invalidation methods, which may cause the page cache not stable
So I think we can simply add a file size to identify that the file is changed.
In LSM-Tree, all modification will generate new files, such file-name reuse is not normal case(as far as I know, only segment compaction), file size is enough to identify the file change.
Currently, there are some useless includes in the codebase. We can use a tool named include-what-you-use to optimize these includes. By using a strict include-what-you-use policy, we can get lots of benefits from it.
1. solved the previous delayed unit test file size is too large (1.7G+) and the unit test link time is too long problem problems
2. Unify all unit tests into one file to significantly reduce unit test execution time to less than 3 mins
3. temporarily disable stream_load_test.cpp, metrics_action_test.cpp, load_channel_mgr_test.cpp because it will re-implement part of the code and affect other tests
#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
1. BlockManager has been added into StorageEngine.
So StorageEngine should be initialized when starting BetaRowset unit test.
2. Cache should not use the same buf to store value, otherwise the address
will be freed twice and crash.
