Added a test with back-to-back backups. This caused issues with the empty CDB file it created (on opening, couldn't cope with last key of empty).
So now backup won't roll the active journal if it is empty.
As the fold functions have been added to get_runner in an ad hoc way,
naturally, given the ongoing development of levelEd to support Riak,
it was difficult for a new user (in this case Quviq) to see what folds
are supported, and with what arguments, and expectations.
This PR is for discussion. It is one of many ways to group, spec, and
document the fold functions.
A test is also added for coverage of range queries.
head_only mode cna be run with_lookup - but there is no L0 index created in this case.
So the L0 index wasn't returning a potition list and the L0 cache wasn't being checked.
Code now checks every position in the L0 cache, when a lookup is attempted in head_only mode.
An issue was spotted. If we use a segment filter in a query, and there are multiple matches within a given slot - only the first match is returned.
Tests didn't detect this. Now they do, and the issue is resolved.
Test takes a long time due to sleep (still need to work on that), but also FoldKeysFun uses ++ rather than [{B, K}|Acc] to extend the list. Order of magnitude speed-up for these queries by changing the way this accumulates
Originally had disabled the ability to lookup individual values when running in head_only mode. This is a saving of about 11% at PUT time (about 3 microseconds per PUT) on a macbook.
Not sure this saving is sufficient enought to justify the extra work if this is used as an AAE Keystore with Bitcask and LWW (when we need to lookup the current value before adjusting).
So reverted to re-adding support for HEAD requests with these keys.
Initial commit to add head_only mode to leveled. This allows leveled to receive batches of object changes, but where those objects exist only in the Penciller's Ledger (once they have been persisted within the Ledger).
The aim is to reduce significantly the cost of compaction. Also, the objects ar enot directly accessible (they can only be accessed through folds). Again this makes life easier during merging in the LSM trees (as no bloom filters have to be created).
Compression can be switched between LZ4 and zlib (native).
The setting to determine if compression should happen on receipt is now a macro definition in leveled_codec.
