## Design
### Trigger
Every time when a rowset writer produces more than N (e.g. 10) segments, we trigger segment compaction. Note that only one segment compaction job for a single rowset at a time to ensure no recursing/queuing nightmare.
### Target Selection
We collect segments during every trigger. We skip big segments whose row num > M (e.g. 10000) coz we get little benefits from compacting them comparing our effort. Hence, we only pick the 'Longest Consecutive Small" segment group to do actual compaction.
### Compaction Process
A new thread pool is introduced to help do the job. We submit the above-mentioned 'Longest Consecutive Small" segment group to the pool. Then the worker thread does the followings:
- build a MergeIterator from the target segments
- create a new segment writer
- for each block readed from MergeIterator, the Writer append it
### SegID handling
SegID must remain consecutive after segment compaction.
If a rowset has small segments named seg_0, seg_1, seg_2, seg_3 and a big segment seg_4:
- we create a segment named "seg_0-3" to save compacted data for seg_0, seg_1, seg_2 and seg_3
- delete seg_0, seg_1, seg_2 and seg_3
- rename seg_0-3 to seg_0
- rename seg_4 to seg_1
It is worth noticing that we should wait inflight segment compaction tasks to finish before building rowset meta and committing this txn.
1.remove quick_compaction's rowset pick policy, call cu compaction when trigger
quick compaction
2. skip tablet's compaction task when compaction score is too small
Co-authored-by: yixiutt <yixiu@selectdb.com>
The mem hook record tracker cannot guarantee that the final consumption is 0, nor can it guarantee that the memory alloc and free are recorded in a one-to-one correspondence.
In the life cycle of a memtable from insert to flush, the memory free of hook is more than that of alloc, resulting in tracker consumption less than 0.
In order to avoid the cumulative error of the upper load channel tracker, the memtable tracker consumption is reset to zero on destructor.
In VCollectIterator&VGenericIterator, use insert_range_from to copy rows
in a block which is continuous to save cpu cost.
If rows in rowset and segment are non overlapping, this whill improve 30%
throughput of compaction.If rows are completely overlapping such as load two
same files, the throughput goes nearly same as before.
Co-authored-by: yixiutt <yixiu@selectdb.com>
1. use rlock in most logic instead of wrlock
2. filter stale rowset's delete bitmap in save meta
3. add a delete_bitmap lock to handle compaction and publish_txn confict
Co-authored-by: yixiutt <yixiu@selectdb.com>
* remove alpha_rowset_meta
* remove alpha rowset related codes in compaction
* remove alpha rowset related codes in RowsetMeta
* fix be ut because some ut use alpha rowsetmeta
* [Schema Change] support fast add/drop column (#49)
* [feature](schema-change) support fast schema change. coauthor: yixiutt
* [schema change] Using columns desc from fe to read data. coauthor: Lchangliang
* [feature](schema change) schema change optimize for add/drop columns.
1.add uniqueId field for class column.
2.schema change for add/drop columns directly update schema meta
Co-authored-by: yixiutt <yixiu@selectdb.com>
Co-authored-by: SWJTU-ZhangLei <1091517373@qq.com>
[Feature](schema change) fix write and add regression test (#69)
Co-authored-by: yixiutt <yixiu@selectdb.com>
[schema change] be ssupport that delete use newest schema
add delete regression test
fix regression case (#107)
tmp
[feature](schema change) light schema change exclude rollup and agg/uniq/dup key type.
[feature](schema change) fe olapTable maxUniqueId write in disk.
[feature](schema change) add rpc iface for sc add column.
[feature](schema change) add columnsDesc to TPushReq for ligtht sc.
resolve the deadlock when schema change (#124)
fix columns from fe don't has bitmap_index flag (#134)
add update/delete case
construct MATERIALIZED schema from origin schema when insert
fix not vectorized compaction coredump
use segment cache
choose newest schema by schema version when compaction (#182)
[bugfix](schema change) fix ligth schema change problem.
[feature](schema change) light schema change add alter job. (#1)
fix be ut
[bug] (schema change) unique drop key column should not light schema
change
[feature](schema change) add schema change regression-test.
fix regression test
[bugfix](schema change) fix multi alter clauses for light schema change. (#2)
[bugfix](schema change) fix multi clauses calculate column unique id (#3)
modify PushTask process (#217)
[Bugfix](schema change) fix jobId replay cause bdbje exception.
[bug](schema change) fix max col unique id repeatitive. (#232)
[optimize](schema change) modify pendingMaxColUniqueId generate rule.
fix compaction error
* fix be ut
* fix snapshot load core
fix unique_id error (#278)
[refact](fe) remove redundant code for light schema change. (#4)
[refact](fe) remove redundant code for light schema change. (#4)
format fe core
format be core
fix be ut
modify fe meta version
fix rebase error
flush schema into rowset_meta in old table
[refactor](schema change) refact fe light schema change. (#5)
delete the change of schemahash and support get max version schema
* modify for review
* fix be ut
* fix schema change test
This PR supports rowset level data upload on the BE side, so that there can be both cold data and hot data in a tablet,
and there is no necessary to prohibit loading new data to cooled tablets.
Each rowset is bound to a `FileSystem`, so that the storage layer can read and write rowsets without
perceiving the underlying filesystem.
The abstracted `RemoteFileSystem` can try local caching strategies with different granularity,
instead of caching segment files as before.
To avoid conflicts with the code in be/src/io, we temporarily put the file system related code in the be/src/io/fs directory.
In the future, `FileReader`s and `FileWriter`s should be unified.
* compaction quickly for small data import #9791
1.merge small versions of rowset as soon as possible to increase the import frequency of small version data
2.small version means that the number of rows is less than config::small_compaction_rowset_rows default 1000
As in issue, the combination and schema change at the same time may lead to version intersection.
Describe the overview of changes.
1. Do not do compaction before schema change is actually executed.
2. Set tablet as bad when it has version intersection.
3. Do not do schema change when it can not find appropriate versions to delete in new tablet.
4. Do not change rowsets after compaction if the rowsets of the tablet has changed.
1. Fix Lru Cache MemTracker consumption value is negative.
2. Fix compaction Cache MemTracker has no track.
3. Add USE_MEM_TRACKER compile option.
4. Make sure the malloc/free hook is not stopped at any time.
Currently, there are 2 status code in BE, one is common/Status.h,
and the other is olap/olap_define.h called OLAPStatus.
OLAPStatus is just an enum type, it is very simple and could not save many informations,
I will unify these code to common/Status.
1. We forgot to check disk capacity when writing data.
2. TODO: the user specified disk capacity is not used now. We need to find a way to use it.
3. Avoid print too much compaction log when there is not suitable version for compaction.
Early Design Documentation: https://shimo.im/docs/DT6JXDRkdTvdyV3G
Implement a new way of memory statistics based on TCMalloc New/Delete Hook,
MemTracker and TLS, and it is expected that all memory new/delete/malloc/free
of the BE process can be counted.
Modify the implementation of MemTracker:
1. Simplify a lot of useless logic;
2. Added MemTrackerTaskPool, as the ancestor of all query and import trackers, This is used to track the local memory usage of all tasks executing;
3. Add cosume/release cache, trigger a cosume/release when the memory accumulation exceeds the parameter mem_tracker_consume_min_size_bytes;
4. Add a new memory leak detection mode (Experimental feature), throw an exception when the remaining statistical value is greater than the specified range when the MemTracker is destructed, and print the accurate statistical value in HTTP, the parameter memory_leak_detection
5. Added Virtual MemTracker, cosume/release will not sync to parent. It will be used when introducing TCMalloc Hook to record memory later, to record the specified memory independently;
6. Modify the GC logic, register the buffer cached in DiskIoMgr as a GC function, and add other GC functions later;
7. Change the global root node from Root MemTracker to Process MemTracker, and remove Process MemTracker in exec_env;
8. Modify the macro that detects whether the memory has reached the upper limit, modify the parameters and default behavior of creating MemTracker, modify the error message format in mem_limit_exceeded, extend and apply transfer_to, remove Metric in MemTracker, etc.;
Modify where MemTracker is used:
1. MemPool adds a constructor to create a temporary tracker to avoid a lot of redundant code;
2. Added trackers for global objects such as ChunkAllocator and StorageEngine;
3. Added more fine-grained trackers such as ExprContext;
4. RuntimeState removes FragmentMemTracker, that is, PlanFragmentExecutor mem_tracker, which was previously used for independent statistical scan process memory, and replaces it with _scanner_mem_tracker in OlapScanNode;
5. MemTracker is no longer recorded in ReservationTracker, and ReservationTracker will be removed later;
For the first, we need to make a parameter to discribe the data is local or remote.
At then, we need to support some basic function to support the operation for remote storage.
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.
We created multiple rowset readers to read data of one tablet,
after one rowset reader has reached EOF, it can be released to
reduce resource (typically memory) consumption.
As the same, we can release segment reader when it reach EOF.
1 Make some MemTracker have reasonable parent MemTracker not the root tracker
2 Make each MemTracker can be easily to trace.
3 Add show level of MemTracker to reduce the MemTracker show in the web page to have a way to control show how many tracker in web page.
* [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
