Adds a CAS logging interface to track mutations of the CAS and action
cache database files. This is designed to aid in the debugging of
data corruption and other issues with the low-level on-disk
representation.
To enable logging, set the environment variable LLVM_CAS_LOG to 1 or 2.
Level 2 includes logging of all allocations inside the index, action
cache, and datapool, which increases the overhead. The log file is
placed inside the top-level directory of the unified cache. For now it
is a human-readable textual format with one line per entry.
Check that action cache references point to valid CAS objects by
ensuring they are contained within the corresponding CAS and also that
the offsets match. This prevents accidentally referencing "dead" index
records that were not properly flushed to disk, which can lead to the
action cache pointing to the wrong data or to garbage data.
rdar://126642956
Add a new abstraction layer UnifiedOnDiskCache that adds new functions
of disk space management and data validation that builds on top of
OnDiskGraphDB and OnDiskKeyValueDB.
Build upon UnifiedOnDiskCache, it is OnDiskCAS that implements
ObjectStore and ActionCache interface for LLVM tools to interact with
CAS storage.
ActionCache is used to store a mapping from CASID to CASID. The current
implementation of the ActionCache can only be used to associate the
key/value from the same hash context.
ActionCache has two operations: `put` to store the key/value and `get`
to
lookup the key/value mapping. ActionCache uses the same TrieRawHashMap
data structure to store the mapping, where is CASID of the key is the
hash to index the map.
While CASIDs for key/value are often associcate with actual CAS
ObjectStore, it doesn't provide the guarantee of the existence of such
object in any ObjectStore.
