Selects a downloaded snapshot of the CRANT synapse table so that
crant_partner_summary(), crant_partners() and crant_synapse_data() can
answer queries locally, without contacting CAVE for synapses. Each snapshot
records the root id of both partners of every synapse at one moment in time.
Usage
crant_use_snapshot(
snapshot = NULL,
version = NULL,
timestamp = NULL,
root = crant_snapshot_root(),
set = TRUE
)Arguments
- snapshot
The snapshot tag, or
"latest"for the most recent snapshot inroot. The default (NULL) chooses one to matchversionortimestamp.- version, timestamp
A CAVE materialisation version or a timestamp (including
"now") to choose the snapshot for.- root
The snapshot folder. Defaults to
crant_snapshot_root().- set
Whether to make this the default snapshot for the session.
Value
When set = TRUE, the previous option values (invisibly, suitable
for passing to options()). Otherwise a list with the snapshot tag,
timestamp and root.
Details
A snapshot folder contains static.parquet (one row per synapse,
with its supervoxels, positions in nm and size) and one sub-folder per
snapshot tag. A full snapshot has the root ids of every synapse; a
checkpoint has only the synapses whose root ids changed since an earlier
snapshot. Queries use DuckDB (from the suggested packages duckdb,
DBI and dbplyr) and only read the parts of the parquet files
that they need. DuckDB uses every core; set the aedes.duckdb_threads
option before the first query to use fewer, e.g. on a shared machine.
The snapshot code currently lives in the aedes package, which must be installed (see the vignette).
When no snapshot is given, the newest one at or before timestamp (or
the time of version) is used, or the newest one of all when neither is
given. Queries for times after the snapshot fetch the edits made since
then from CAVE (see crant_synapse_data()).
If there is no snapshot in root, you are asked whether to download one
with crant_download_snapshot() (in an interactive session) or get an
error saying how to.
Every few hours (the crantr.snapshot_check_hours option, default 6;
Inf turns this off) it also downloads any new checkpoints that have
been published. A new full snapshot is only announced, since it is
larger: fetch it with crant_download_snapshot().
Examples
if (FALSE) { # \dontrun{
crant_use_snapshot()
# now answered locally
crant_partner_summary("576460752684030043")
} # }