= Large Area Processing =

= Database tables =

The '''lapRun''' table defines and groups the reprocessing of a single projection cell

|| '''name'''            || '''type'''   || '''note''' ||
|| lap_id          || int    ||             ||
|| seq_id          || int    || ||
|| tess_id         || string || ||
|| projection_cell || string || ||
|| filter          || string || ||
|| state           || string || 'new' if still running, 'full' if complete ||
|| registered      || date   || date lapRun was defined ||
|| fault           || int    || ||
|| label           || string || ||
|| quick_sass_id   || int    || stackAssociation id of the quickstack for this run ||
|| final_sass_id   || int    || stackAssociation id of the final stack for this run ||
|| dist_group      || string || distribution group to give to all dependents ||

The '''lapExp''' table defines the pool of exposures, and associates them with the lapRuns that use them

|| '''name'''       || '''type'''   || '''note''' ||
|| lap_id     || int    || ||
|| exp_id     || int    || ||
|| chip_id    || int    || chip_id of the processing of exp_id used in this run ||
|| pair_id    || int    || chip_id of the companion exposure for a pairwise diff ||
|| private    || bool   || this exp_id/chip_id set is only available to this run ||
|| pairwise   || bool   || this chip_id will be pairwise diffed against pair_id ||
|| active     || bool   || this exp_id/chip_id is currently in use by this run ||
|| data_state || string || ||

The '''lapSequence''' table groups a set of lapRuns together into a complete sample of the sky.

|| '''name'''        || '''type'''   || '''note''' ||
|| seq_id      || integer ||             ||
|| description || string  ||             ||

= Processing Steps =

== Sequence definition ==

A `lapSequence` is defined by calling `laptool -definesequence -name "unique name" -description "long description explaining what this sequence is"`.  `laptool -listsequence` prints the information about sequences in the metadata format. 

== Run definition ==

A new `lapRun` is defined by calling `laptool -definerun -seq_id S -projection_cell PC_NAME -ra RA_CENTER -decl DEC_CENTER -radius R -filter F -label L`.  This adds a row to `lapRun`, and then creates a row in `lapExp` for each exposure that falls within the area on the sky defined by the -ra/-decl/-radius options.  If these exposures have been previously processed (and therefore have a row in `lapExp` associated with a different `lapRun`), the `chip_id` for the new lapExp is copied from that previous entry, provided that the `private` flag is not true.  

== Chip-Warp processing ==

Defining the run does not queue chipRuns for those exposures that have not been processed previously.  This is done by the `lap_science.pl --chip_mode --lap_id LAP` command.  This script calls `laptool -pendingexp -lap_id LAP` which returns a list of all the exposures included in this `lapRun`.  Each exposure is checked, and a `chipRun` queued if the `chip_id` entry is blank.

This stage also defines the pairs for differencing, using the object and comment fields to organize the pairs as is done in nightly science.  If a pair is found, the associated `pair_id` fields point at the `chip_id` of the companion exposure, and the `pairwise` flag is set to true.  If a pair is not found, `pair_id` is left as NULL, `pairwise` is set to false, and `private` is set to true.  This ensures that the difference against the quickstack will not be used by other `lapRun`s.

Once all the chips have been queued, the state of the `lapRun` will be polled using the `lap_science.pl --status --lap_id LAP`.  This calls `laptool -exposures -lap_id LAP` which returns the status of each exposure at the chip, camera, fake, warp, diff, and magic stages.  In addition to gauging completion, exposure pairs are checked against each other to confirm that no faults have occurred.  If one member of a pair has an unrecoverable fault, that entry is marked with `data_state` = 'drop', and is no longer used.  The companion of that unrecoverable exposure is set to be private so it will be diffed against the quickstack.  

Setting the `lapExp` to private "steals" this processing run away from any other `lapRun` that may want to use it. If `lap_science.pl` detects that another `lapExp` with this `exp_id`/`chip_id` set has `private` = true, then it will requeue a `chipRun` for that `exp_id`, and record the new `chip_id` for itself, and set `private` = true.

The script will also check the status of any stacks via the `laptool -stacks -lap_id LAP` which returns the status of all associated stacks for this `lapRun`.  This information is used to set a pair of flags for both the quick and final stacks: the `defined_`flag notes that stacks have been queued, and the `have_` flag notes that the stacks have completed and may be used.

Using the information about the exposures and stacks for this `lapRun`, `lap_science.pl` will decide what the next step of the processing will be.  After all exposures have a `warpRun.state` of full (or have been dropped due to quality), `lap_science.pl` checks which step is most appropriate:

=== Quick stacks ===

If any `lapExp` has `private` = true, then a quickstack is needed.  If `defined_quick` is false, the quickstack is queued, and the appropriate `stackAssociation.sass_id` is recorded as `lapRun.quick_sass_id`.  

=== Diffs ===

If no `lapExp` has `private` = true, and they all have valid `pair_id` values, then they will all be pairwise diffed.  If any `lapExp` has `private` = true, and `have_quick` is true (marking that the quickstack has finished), then the quickstack diff for that exposure will be queued as well.

=== Final stacks ===

Once the diffs have completed, the regular stdscience/distribution tools will be used to process all data through the magic and destreak steps.  Once these have completed, the `warpRun.magicked` value is used to determine if a `lapExp` is ready for the final stacking stage.  If all `lapExp`s have a non-zero `magicked` value, or have a data_state = 'drop', and `defined_final` is false, then the final stack is queued, and the appropriate `stackAssociation.sass_id` is recorded as `lapRun.final_sass_id`.

=== Cleanup ===

Once the final stacks have completed, the `lapRun` is also complete.  If have_final is true, then `lapRun.state` is set to 'full', and all `lapExp.active` is set to false.  Periodically, `lap_science.pl --cleanup` will poll all `lapExp`, and if all `lapExp` with a given `chip_id` have `active` = false, then the products of all stages generated from that `chip_id` will be marked for cleanup (`STAGE.label = 'goto_cleaned'`, `STAGE.state = 'goto_cleaned'`).

== Proposed Changes ==

=== Update ===

Even after cleanup, `lapExp` still records whether an exposure has been fully processed previously.  Therefore, instead of queuing a new `chipRun` for this exposure, the data products may be updated instead.  This will be faster than starting from scratch.  Implementing this is not significantly difficult, as it requires only relaxing the state restriction in `laptool -definerun` and having `lap_science.pl` know how to update a `lapExp` with `STAGE.state = 'cleaned'`.

=== Complete Private diffs ===

If an unpaired `lapExp` spans multiple `projection_cell`s, then if we make the requirement that the quickstacks associated with all of the `projection_cell`s are complete before diffing, then we do not need to make that `lapExp` private.  The difference can then be done across the entire image, instead of only over the overlapping area.  This will reduce the amount of processing required, but will likely increase the mask fraction for that `lapExp`.