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.
This patch:
1. Removes the option to declare uncompressed columns (set columnstore_compression_type = 0).
2. Ignores [COMMENT '[compression=0] option at table or column level (no error messages, just disregard).
3. Removes the option to set more than 2 extents per file (ExtentsPreSegmentFile).
4. Updates rebuildEM tool to support up to 10 dictionary extent per dictionary segment file.
5. Adds check for `DBRootStorageType` for rebuildEM tool.
6. Renamed rebuildEM to mcsRebuildEM.
* TEXT and BLOB now have separate identifiers internally
* TEXT columns are identified as such in system catalog
* cpimport only requires hex input for BLOB, not TEXT
Date limit of year 1400 was used due to Boost's limits.
This patch strips out the use of Boost for date handling and sets the
lower limit to year 1000.
