This CL includes:
* Change the column metadata to a tree structure.
* Refactor the segment_v2.ColumnReader and sgment_v2.ColumnWriter to support complex type.
* Implements the reading and writing of array type.
We make all MemTrackers shared, in order to show MemTracker real-time consumptions on the web.
As follows:
1. nearly all MemTracker raw ptr -> shared_ptr
2. Use CreateTracker() to create new MemTracker(in order to add itself to its parent)
3. RowBatch & MemPool still use raw ptrs of MemTracker, it's easy to ensure RowBatch & MemPool destructor exec
before MemTracker's destructor. So we don't change these code.
4. MemTracker can use RuntimeProfile's counter to calc consumption. So RuntimeProfile's counter need to be shared
too. We add a shared counter pool to store the shared counter, don't change other counters of RuntimeProfile.
Note that, this PR doesn't change the MemTracker tree structure. So there still have some orphan trackers, e.g. RowBlockV2's MemTracker. If you find some shared MemTrackers are little memory consumption & too time-consuming, you could make them be the orphan, then it's fine to use the raw ptr.
After replacing Arena with MemPool, we can achieve one copy for string
value read from segment v2. We can exchange MemPool's chunk between
RowBlockV2 and RowBlock. This change only replace Arena, this work will
be done in other change list.
Currently, we have Field and ColumnSchema to access column data in a
row. These two classes are mostly the same. So we should unify these to
one class. Now, Field has offset information, which is an row attribute,
so we remove offset in Field.
RowCursor now has some logic which belong to Schema, so in this patch I
add Schema attribute to RowCursor to make RowCursor simple. After this
change, only Schema will handle Field/ColumnSchema.
I extract some logic from RowCursor to be/src/olap/row.h, then we can
use same logic to handle different types of row. Each type of row has
same function that to get Cell of this row. A cell represent a column
content with a null indicator.
Use RowwiseIterator to uniform all data fetch in storage engine.
All objects in storage engine can be read in iterator format.
For example: Segment, Rowset.
This patch implement two generic iterators: UnionRowwiseIterator,
MergeRowwiseIterator. These two class will add iterator as its inputs.
To implement iterators, we define a new class RowBlockV2, all data read
from iterator is in this format. We define a new class other than use
old version's RowBlock is because we want to keep old code work
normally.
