* fix(rowgroup): RGData now uses uint64_t counter for the fixed sizes columns data buf.
The buffer can utilize > 4GB RAM that is necessary for PM side join.
RGData ctor uses uint32_t allocating data buffer.
This fact causes implicit heap overflow.
* feat(bytestream,serdes): BS buffer size type is uint64_t
This necessary to handle 64bit RGData, that comes as
a separate patch. The pair of patches would allow to
have PM joins when SmallSide size > 4GB.
* feat(bytestream,serdes): Distribute BS buf size data type change to avoid implicit data type narrowing
* feat(rowgroup): this returns bits lost during cherry-pick. The bits lost caused the first RGData::serialize to crash a process
This patch improves handling of NULLs in textual fields in ColumnStore.
Previously empty strings were considered NULLs and it could be a problem
if data scheme allows for empty strings. It was also one of major
reasons of behavior difference between ColumnStore and other engines in
MariaDB family.
Also, this patch fixes some other bugs and incorrect behavior, for
example, incorrect comparison for "column <= ''" which evaluates to
constant True for all purposes before this patch.
The idea is relatively simple - encode prefixes of collated strings as
integers and use them to compute extents' ranges. Then we can eliminate
extents with strings.
The actual patch does have all the code there but miss one important
step: we do not keep collation index, we keep charset index. Because of
this, some of the tests in the bugfix suite fail and thus main
functionality is turned off.
The reason of this patch to be put into PR at all is that it contains
changes that made CHAR/VARCHAR columns unsigned. This change is needed in
vectorization work.
