The type for indexes.

The type for keys.

The type for values.

The type for caches of index instances.

Construct a new empty cache of index instances.

The constructor for indexes.

• parameter flush_callback

  A function to be called before any new bindings are persisted to disk (including both automatic flushing and explicit calls to flush or close).

This can be used to ensure certain pre-conditions are met before bindings are persisted to disk. (For instance, if the index bindings are pointers into another data-structure d, it may be necessary to flush d first to avoid creating dangling pointers.)

• parameter cache

  used for instance sharing.

• parameter fresh

  whether an existing index should be overwritten.

• parameter read_only

  whether read-only mode is enabled for this index.

• parameter throttle

  the strategy to use when the cache are full and and async in already in progress. Block_writes (the default) blocks any new writes until the merge is completed. Overcommit_memory does not block but continues to fill the (already full) cache.

• parameter log_size

  the maximum number of bindings in the `log` IO.

• parameter lru_size

  the maximum number of recently-read index bindings kept in memory. Defaults to 30_000.

clear t clears t so that there are no more bindings in it.

find t k is the binding of k in t.

mem t k is true iff k is bound in t.

replace t k v binds k to v in t, replacing any existing binding of k.

If overcommit is true, the operation does not triger a merge, even if the caches are full. By default overcommit is false.

filter t p removes all the bindings (k, v) that do not satisfy p. This operation is costly and blocking.

Iterates over the index bindings. Limitations:

• Order is not specified.
• In case of recent replacements of existing values (since the last merge), this will hit both the new and old bindings.
• May not observe recent concurrent updates to the index by other processes.

Flushes all internal buffers of the IO instances.

• Passing ~no_callback:() disables calling the flush_callback passed to v.
• If with_fsync is true, this also flushes the OS caches for each IO instance.

Closes all resources used by t, flushing any internal buffers in the instance.

If immediately is passed, this operation will abort any ongoing background processes. This guarantees not to corrupt the store, but may require additional work to be done on the next startup.

sync t syncs a read-only index with the files on disk. Raises RW_not_allowed if called by a read-write index.

is_merging t returns true if t is running a merge. Raises RO_not_allowed if called by a read-only index.

merge t forces a merge for t.

If there is no merge running, this operation is non-blocking, i.e. it returns immediately, with the merge running concurrently.

If a merge is running already, this operation blocks until the previous merge is complete. It then launches a merge (which runs concurrently) and returns.

try_merge is like merge but is a no-op if the number of entries in the write-ahead log is smaller than log_size.

Offline fsck-like utility for checking the integrity of Index stores built using this module.