# moc-set
A command-line tool to build, update and query a **persistent** set of
Multi-Order Coverages maps (MOCs), see [this IVOA standard](https://ivoa.net/documents/MOC).
## About
Query a set of S-MOCs pre-saved in a single large binary file.
The file can be seen as a persistent cache preventing
from having to open/read/parse a possible large set of FITS files.
A `moc-set` can be updated by adding or removing MOCs from it, without having
to re-build the full binary file (except from time to time using the `purge` command).
It is built in such a way that read operations are allowed while updating (add, remove, change status, purge)
the binary file, but a write operation immediately fails (return status != 0) if another write operation
is already ongoing.
## Used by
MOC set in used:
* in production in [VizieR](https://vizier.u-strasbg.fr/viz-bin/VizieR) when querying a cone
on the `> 16_000` catalogues
* in an ongoing project leading by [@lmichel](https://github.com/lmichel) to look for XMM FOVs intersecting a user define region.
## Similar to the [CDS MOC Server](http://alasky.unistra.fr/MocServer/query).
The [CDS MOC Server](http://alasky.unistra.fr/MocServer/query) additionally stores metadata information associated
to each MOC, allows queries with constraints on those metadata, and supports T-MOCs and ST-MOCs in addition to S-MOCs.
So, `moc-set` offers functionalities similar to **a sub-part of** the MOC Server functionalities
(except for T-MOCs and ST-MOCs, one could build a MOC Server like service based on `moc-set`,
using an additional mechanism to store and filter metadata).
The MOC Server is implemented in Java. All information used by the MOC Server are loaded
in memory at service startup. To speed up the starting time, the MOC Server also resort on a binary dump,
needing synchronisation mechanisms with the running server data when the list of MOCs is updated.
`moc-set` has primarily been developed for VizieR needs: lighter/simpler version of the MOC server, with
less information needed (VizieR already store catalogues metadata), system programming language with no runtime,
possibly less memory available, ...
## Install
### From pypi for python users
MOCSet is available in [pypi](https://pypi.org/project/moc-set),
you can thus install the `mocset` executable using `pip`:
```bash
pip install -U moc-set
mocset --help
```
### Debian package
Download the last `mocset_vxx_yyy.deb` corresponding to your architecture
(`x86_64_musl` has the most chances to fit your needs)
from the [github release page](https://github.com/cds-astro/cds-moc-rust/releases).
Install the `.deb` by clicking on it or using the command line:
```bash
sudo dpkg -i mocset_vxx_yyy.deb
sudo apt-get install -f
```
Then you can use the tool:
```bash
mocset
man mocset
```
You can uninstall using, e.g.:
```bash
sudo dpkg -r $(dpkg -f mocset_vxx_yyy.deb Package)
```
### Pre-compile binaries for MacOS, Linux and Windows
Download the last `mocset-vxx_yyy.tar.gz` corresponding to your architecture
from the [github release page](https://github.com/cds-astro/cds-moc-rust/releases).
You probably want ot use:
* Linux: `mocset-vxx-x86_64-unknown-linux-musl.tar.gz`
* MacOS: `mocset-vxx-x86_64-apple-darwin.tar.gz`
* Windows: `mocset-vxx-.zip`
WARNING: for linux, use [`musl`](https://en.wikipedia.org/wiki/Musl) instead of `gnu` (high chances of incompatibility in the latter case)
The tar contains a single executable binary file.
```bash
tar xzvf mocset-vxx-yyy.tar.gz
./mocset
```
### Compile from source code
[Install rust](https://www.rust-lang.org/tools/install)
(and check that `~/.cargo/bin/` is in your path),
or update the Rust compiler with:
```bash
rustup update
```
Clone the [moc lib rust](https://github.com/cds-astro/cds-moc-rust) project:
```dtd
git clone https://github.com/cds-astro/cds-moc-rust
```
Install from using `cargo`:
```bash
cargo install --path crates/set
```
or
```
RUSTFLAGS='-C target-cpu=native' cargo install --path crates/set
```
## Usage
Exec `mocset --help` to get the help message:
```
> mocset --help
Command-line tool to build, update and query a persistent set of HEALPix Multi-Order Coverages maps (MOCs)
Usage: mocset <COMMAND>
Commands:
make Make a new mocset
append Append the given MOCs to an existing mocset
chgstatus Change the status flag of the given MOCs identifiers (valid, deprecated, removed)
purge Purge the mocset removing physically the MOCs flagged as 'removed'
list Provide the list of the MOCs in the mocset and the associated flags
query Query the mocset
union Union of all MOCs in the moc-set matching a given region
extract Extracts a MOC from the given moc-set
help Print this message or the help of the given subcommand(s)
Options:
-h, --help Print help
-V, --version Print version
```
### MOC set creation
Simply list in a csv file a set of identifier (integer in `[0, 281_474_976_710_655]`),
and MOC FITS file path. See e.g the file [moclist.txt](resources/tests/moclist.txt):
```bash
1,data/CDS_B_bax_bax.fits
2,data/CDS_I_172_irs.fits
3,data/CDS_I_274_ccdm.fits
4,data/CDS_I_42_catalog.fits
5,data/CDS_II_203A_faint.fits
6,data/CDS_II_261_GOODS_S.fits
7,data/CDS_II_339_summary.fits
8,data/CDS_II_97_ans.fits
9,data/CDS_III_206_orion.fits
10,data/CDS_III_43_main.fits
...
```
Then execute `moc-set` from the `mocset` command:
```bash
> mocset make --n128 3 --moc-list moclist.txt --delimiter , mocset.bin
```
or from the source code, [installing](https://www.rust-lang.org/tools/install) the Rust compiler (including Cargo):
```bash
> cargo run --release -- make --n128 3 --moc-list moclist.txt --delimiter , mocset.bin
```
To build the moc-set binary file `mocset.bin`.
The total number of MOCs that can be stored in the file equals `n128 * 128 - 1 (so 383 in the example above, since n128=3).
See the help message for more details:
```
> mocset make --help
Make a new mocset
Usage: mocset make [OPTIONS] <FILE>
Arguments:
<FILE> Output file, storing the MOC set
Options:
-l, --moc-list <FILE> Input file containing the 'moc_id moc_path' list (default: read from stdin) 'moc_id' must be a positive integer smaller than 281_474_976_710_655 (can be stored on 6 bytes). Use a negative value to flag as deprecated
-d, --delimiter <SEPARATOR> Delimiter used to separate the moc identifier from the moc path [default: " "]
-n, --n128 <N128> n x 128 - 1 = number of MOCs that can be stored in this moc set [default: 1]
-h, --help Print help
```
### List the content of a MOC set
Simply use `mocset list`:
```
> mocset list mocset.bin
id,status,depth,n_ranges,byte_size
1,valid,11,1673,13384
2,valid,11,36022,288176
3,valid,11,55470,443760
4,valid,11,587,4696
5,valid,11,534,4272
6,valid,11,17,136
...
```
* `status`: can be `valid`, `deprecated` or `removed`
* `n_ranges`: number of ranges in the MOC
* `byte_size`: size of the MOC stored in the MOC set (in bytes)
See the help message:
```
> mocset list --help
Provide the list of the MOCs in the mocset and the associated flags
Usage: mocset list [OPTIONS] <FILE>
Arguments:
<FILE> The moc-set to be read
Options:
-r, --ranges Print byte ranges instead of byte_size
-h, --help Print help
```
### Querying a MOC set
See the help to get the different query modes:
```
> mocset query --help
Query the mocset
Usage: mocset query [OPTIONS] <FILE> <COMMAND>
Commands:
pos Single position
cone A cone, i.e. a position with a small area around (approximated by a MOC)
moc The given MOC (you create a moc using moc-cli and pipe it into moc-set)
help Print this message or the help of the given subcommand(s)
Arguments:
<FILE> The moc-set to be read
Options:
-d, --add-deprecated Also selects MOCs flagged as deprecated
-c, --print-coverage Print in output the sky fraction (in '[0.0, 1.0]') covered by each selected MOC
-p, --parallel <PARALLEL> Switch on multi-threading, with 'parallel' threads (made for SSD, not HDD)
-h, --help Print help
```
#### Query for a single position
To obtain the list of the MOCs containing a the position 90.0 +0.0 (in decimal degrees), use:
```bash
> mocset query moclist.bin pos 90.0 +0.0
id
161
```
The result is the list of the identifier of the MOC covering the input position (only one MOC, with identifier 161 in our example).
See the full help:
```
> mocset query pos --help
Single position
Usage: mocset query <FILE> pos <LON_DEG> <LAT_DEG>
Arguments:
<LON_DEG> Longitude of the cone center (in degrees)
<LAT_DEG> Latitude of the cone center (in degrees)
Options:
-h, --help Print help
```
#### Query for a cone
To obtain the list of the MOCs overlapping the cone of center 90.0 +0.0 and having a radius of 320 arcsec, use:
```bash
> mocset query mocset.bin cone 90.0 +0.0 320.0 --precision 5
id
2
3
35
161
```
`--precision` is optional, its default value is 2:
* at a `precision` of 0, `mocset` transforms the input cone in a MOC
containing 1 to 9 values.
* at a `precision` of 1, `mocset` transforms the input cone in a MOC
containing 1 to `9x4` values.
* at a `precision` of `n`, `mocset` transforms the input cone in a MOC
containing 1 to `9x4^n` values.
See the help:
```
> mocset query cone --help
A cone, i.e. a position with a small area around (approximated by a MOC)
Usage: mocset query <FILE> cone [OPTIONS] <LON_DEG> <LAT_DEG> <R_ARCSEC>
Arguments:
<LON_DEG> Longitude of the cone center (in degrees)
<LAT_DEG> Latitude of the cone center (in degrees)
<R_ARCSEC> Radius of the cone (in arcseconds)
Options:
-p, --precision <PREC> MOC precision; 0: depth 'd' at which the cone is overlapped by 1 to max 9 cells; 1: depth 'd' + 1; n: depth 'd' + n [default: 2]
-i, --included Returns MOCs containing the whole cone MOC (instead of overlapping only)
-h, --help Print help
```
#### Query for a MOC
To obtain the list of the MOCs overlapping the MOC stored in a given FITs file, e.g the MOC of XMM4 DR9, use:
```
> mocset query mocset.bin moc YOUR_PATH/CDS_IX_59_xmm4dr9s.fits
id
1
2
3
4
5
6
7
8
9
10
...
```
You may also use a MOC generate on the fly using [moc-cli](https://github.com/cds-astro/cds-moc-rust/tree/main/crates/cli)
```
> moc from polygon 5 "(0.0,0.0),(10.0,0.0),(0.0,10.0)" ascii | mocset query mocset.bin moc - --format ascii
id
1
2
3
4
7
8
13
26
27
35
36
60
63
...
```
See the help
```
> mocset query moc --help
The given MOC (you create a moc using moc-cli and pipe it into moc-set)
Usage: mocset query <FILE> moc [OPTIONS] <FILE>
Arguments:
<FILE> Path of the input MOC file (or stdin if equals "-")
Options:
-f, --format <INPUT_FMT> Format of the input MOC ('ascii', 'json' or 'fits') [default: guess from the file extension]
-i, --included Returns MOCs containing the whole given MOC (instead of overlapping)
-h, --help Print help
```
### Query from a STC-S region
You can query from a STC-S region using `moc-cli`:
```bash
echo "Intersection ICRS (
Polygon 272.536719 -19.461249 272.542612 -19.476380 272.537389 -19.491509 272.540192 -19.499823
272.535455 -19.505218 272.528024 -19.505216 272.523437 -19.500298 272.514082 -19.503376
272.502271 -19.500966 272.488647 -19.490390 272.481932 -19.490913 272.476737 -19.486589
272.487633 -19.455645 272.500386 -19.444996 272.503003 -19.437557 272.512303 -19.432436
272.514132 -19.423973 272.522103 -19.421523 272.524511 -19.413250 272.541021 -19.400024
272.566264 -19.397500 272.564202 -19.389111 272.569055 -19.383210 272.588186 -19.386539
272.593376 -19.381832 272.596327 -19.370541 272.624911 -19.358915 272.629256 -19.347842
272.642277 -19.341020 272.651322 -19.330424 272.653174 -19.325079 272.648903 -19.313708
272.639616 -19.311098 272.638128 -19.303083 272.632705 -19.299839 272.627971 -19.289408
272.628226 -19.276293 272.633750 -19.270590 272.615109 -19.241810 272.614704 -19.221196
272.618224 -19.215572 272.630809 -19.209945 272.633540 -19.198681 272.640711 -19.195292
272.643028 -19.186751 272.651477 -19.182729 272.649821 -19.174859 272.656782 -19.169272
272.658933 -19.161883 272.678012 -19.159481 272.689173 -19.176982 272.689395 -19.183512
272.678006 -19.204016 272.671112 -19.206598 272.664854 -19.203523 272.662760 -19.211156
272.654435 -19.214434 272.652969 -19.222085 272.656724 -19.242136 272.650071 -19.265092
272.652868 -19.274296 272.660871 -19.249462 272.670041 -19.247807 272.675533 -19.254935
272.673291 -19.273917 272.668710 -19.279245 272.671460 -19.287043 272.667507 -19.293933
272.669261 -19.300601 272.663969 -19.307130 272.672626 -19.308954 272.675225 -19.316490
272.657188 -19.349105 272.657638 -19.367455 272.662447 -19.372035 272.662232 -19.378566
272.652479 -19.386871 272.645819 -19.387933 272.642279 -19.398277 272.629282 -19.402739
272.621487 -19.398197 272.611782 -19.405716 272.603367 -19.404667 272.586162 -19.422703
272.561792 -19.420008 272.555815 -19.413012 272.546500 -19.415611 272.537427 -19.424213
272.533081 -19.441402
Not (Polygon 272.511081 -19.487278 272.515300 -19.486595 272.517029 -19.471442
272.511714 -19.458837 272.506430 -19.459001 272.496401 -19.474322 272.504821 -19.484924)
Not (Polygon 272.630446 -19.234210 272.637274 -19.248542 272.638942 -19.231476 272.630868 -19.226364)
)" | moc from stcs 14 - ascii | mocset query mocset.bin moc - --format ascii
```
#### Generic parameter
For all queries, the option `--add-deprecated` (or `-d`) add the MOCs flagged as deprecated in
the output, e.g.:
```bash
mocset query --add-deprecated moclist.bin pos 90.0 +0.0 --precision 5
```
### Updating a MOC set
You can:
* `chgstatus` change the status of a MOC in the MOC set to flag it as `deprecated` or back to `valid`,
or as `removed` (WARNING: once removed, a MOC cannot be flagged back as `deprecated` or `valid`)
* `append` a new MOC at the end of the MOC set, the ID of a removed MOC can be reused
* `purge` a MOC set to physically remove all MOCs flagged as `removed`.
This process basically re-write the whole MOC set file.
Example of usage of `chgstatus`
```
> mocset list mocset.bin
id,status,depth,n_ranges,byte_size
1,valid,11,1673,13384
2,valid,11,36022,288176
...
> mocset chgstatus mocset.bin 1 deprecated
> mocset list mocset.bin
id,status,depth,n_ranges,byte_size
1,deprecated,11,1673,13384
2,valid,11,36022,288176
...
> mocset chgstatus mocset.bin 1 valid
> mocset list mocset.bin
id,status,depth,n_ranges,byte_size
1,valid,11,1673,13384
2,valid,11,36022,288176
...
> mocset chgstatus mocset.bin 1 removed
> mocset list mocset.bin
id,status,depth,n_ranges,byte_size
1,removed,11,1673,13384
2,valid,11,36022,288176
...
```
Example of usage of `append`:
```
> mocset append mocset.bin 3000 MY_PATH/my_new_moc.fits
```
Example of usage of `purge`:
```
> mocset purge mocset.bin
```
Help messages:
```
> mocset chgstatus --help
Change the status flag of the given MOCs identifiers (valid, deprecated, removed)
Usage: mocset chgstatus <FILE> <NEW_STATUS> [IDS]...
Arguments:
<FILE> The moc-set to be updated
<NEW_STATUS> New status flag to be set
[IDS]... Comma separated list of identifiers of the MOCs we want to modify the flag
Options:
-h, --help Print help
```
```
> mocset append --help
Append the given MOCs to an existing mocset
Usage: mocset append <FILE> <ID> <MOC_PATH>
Arguments:
<FILE> The moc-set to be updated
<ID> Identifier of the MOC we want to append. 'moc_id' must be a positive integer smaller than 281_474_976_710_655 (can be stored on 6 bytes). Use a negative value to flag as deprecated
<MOC_PATH> Path of the MOC to be append
Options:
-h, --help Print help
```
```
> mocset purge --help
Purge the mocset removing physically the MOCs flagged as 'removed'
Usage: mocset purge [OPTIONS] <FILE>
Arguments:
<FILE> The moc-set file to be purge
Options:
-n, --n128 <N128> n x 128 - 1 = number of MOCs that can be stored in this purged moc set, if larger than the current value
-h, --help Print help
```
# Implementation information
## Principle
We resort on mapped files and the system disk cache.
Although the first `moc-set` query may still be quite long,
the performances of subsequent queries will depend on the ability
of the system to keep the file's data in the disk cache.
### Remark
If used on a server with a lot of I/O, the data may not stay in the disk cache for long.
If we nevertheless want to always answer quickly, there is at least three options:
* write a daemon loading the full dataset in memory
* create a VM (or a docker?) containing only the `moc-set` tool
* my favourite one: use shared memory, resorting e.g. on the [shared_memory crate](https://crates.io/crates/shared_memory)
### File structure
The structure of the file is made of two main blocks:
* a fixed length header, made of
+ a fixed length metadata
+ a fixed length cumulative byte index
* a extensible data part
#### Metadata part
A fixed size (chosen at creation) buffer of `n` `u64` elements.
* the first `u64` contains an indication on the buffer size
* all other `u64` values, one per MOC in the `moc-set`, are made of 3 components:
+ a `u8` flag taking 4 possible values (only 2 bits are used, 6 are remaining):
- `Valid` MOC
- `Deprecated` MOC
- `Removed` MOC
- `Free` slot
+ the depth of the MOC, stored on `u8 (max depth = 64, thus 2 bits are remaining and could be used)
+ the MOC identifier, stored on the 6 remaining bytes.
We stop reading the metadata when we encounter the first `Free` flag.
The file can store `n - 1` MOCs.
#### Cumulative byte index
A fixed size (chosen at creation) buffer of `n` `u64` elements.
* the first `u64` contains the byte size of the header, i.e. the size of the file with no data
it also correspond to the starting byte of the first MOC that will be inserted in the `moc-set`;
* all other elements at index `i` contains the size of the file if only storing the
$i+1$ first MOCs.
To get the size (in bytes) of the MOC at index `i`, we can simply perform the operation:
`cumulIndex[i + 1] - cumulIndex[i]`.
#### Data part
A simple concatenation of the MOCs ranges.
According to the depth of each MOC, the ranges are either ranges of `u32` or ranges of `u64`.
### Updates and Reading while writing
The only MOC information that can be modified (re-written) is its status flag.
But the status flag is coded on a single byte and a CPU read and write single bytes atomically.
Although, several cores may see the byte in a different state, it is not critical:
a MOC flagged as 'deprecated' or 'deleted' is still physically stored in the `moc-set`,
and we can accept a small delay in changing its state.
* Read operation order
+ do not need a read lock
+ read the metadata part of the header
+ read the cumulative bytes index in the header
+ read the MOC(s)
* Write Operation order
+ ask for a write lock (create a .lock file)
+ append the new MOC(s) to the end of the file
+ append the new entries to the cumulative bytes index
+ possibly update the flag of existing MOCs and append new entries to the end of the header
The header, i.e. both the metadata and the cumulative byte index, is of fixed size,
with free space reserved at file creation.
If a problem occurs while writing, the update is simply going to be ignored
(except the part written in the meta): at the next write operation, if the meta
has not been written (and it is the last part to be written), the code assumes
that the cumulative index beyond the know meta elements is free, the same for the
data byte beyond the last known cumulative index byte.
If a process is reading while another is writing, the newly written part will also
simply be ignored if the metadata part has not yet been updated/written.
It works well because we only append new MOCs (we never delete information),
we only update metadata to flag a MOC as removed of deprecated, and we
respect the read/write order as described above.
#### Mocset file before adding a new MOC
#### Add a new moc step 1/3
#### add a new moc step 2/3
#### add a new moc step 3/3
#### Mocset file after having added a new MOC
#### Purge
The purge operation is the only one removing physically stored MOCs.
It actually consists in building a new `moc-set`, removing the MOCs flagged as removed,
in a temporary file, and then making a move replacing the previous `moc-set`
by the new one.
The `purge` operation uses a write lock.
## Recall
* Drop linux disk cache, in root mode: `sync; echo 3 > /proc/sys/vm/drop_caches`
* Build for being compatible with a large range of systems, avoiding the GLIBC version error
(see [this post](https://stackoverflow.com/questions/63724484/build-and-bind-against-older-libc-version)):
> cargo build --target x86_64-unknown-linux-musl
Raw data
{
"_id": null,
"home_page": "https://github.com/cds-astro/cds-moc-rust/tree/main/crates/set",
"name": "moc-set",
"maintainer": null,
"docs_url": null,
"requires_python": "",
"maintainer_email": null,
"keywords": "healpix,moc",
"author": "F.-X. Pineau <francois-xavier.pineau@astro.unistra.fr>",
"author_email": "F.-X. Pineau <francois-xavier.pineau@astro.unistra.fr>",
"download_url": null,
"platform": null,
"description": "# moc-set\n\nA command-line tool to build, update and query a **persistent** set of\nMulti-Order Coverages maps (MOCs), see [this IVOA standard](https://ivoa.net/documents/MOC).\n\n## About\n\nQuery a set of S-MOCs pre-saved in a single large binary file. \nThe file can be seen as a persistent cache preventing\nfrom having to open/read/parse a possible large set of FITS files. \nA `moc-set` can be updated by adding or removing MOCs from it, without having \nto re-build the full binary file (except from time to time using the `purge` command).\nIt is built in such a way that read operations are allowed while updating (add, remove, change status, purge) \nthe binary file, but a write operation immediately fails (return status != 0) if another write operation \nis already ongoing. \n\n\n## Used by\n\nMOC set in used:\n* in production in [VizieR](https://vizier.u-strasbg.fr/viz-bin/VizieR) when querying a cone\n on the `> 16_000` catalogues\n* in an ongoing project leading by [@lmichel](https://github.com/lmichel) to look for XMM FOVs intersecting a user define region.\n\n\n## Similar to the [CDS MOC Server](http://alasky.unistra.fr/MocServer/query). \n\nThe [CDS MOC Server](http://alasky.unistra.fr/MocServer/query) additionally stores metadata information associated \nto each MOC, allows queries with constraints on those metadata, and supports T-MOCs and ST-MOCs in addition to S-MOCs. \n\n\nSo, `moc-set` offers functionalities similar to **a sub-part of** the MOC Server functionalities\n(except for T-MOCs and ST-MOCs, one could build a MOC Server like service based on `moc-set`, \nusing an additional mechanism to store and filter metadata).\n\nThe MOC Server is implemented in Java. All information used by the MOC Server are loaded \nin memory at service startup. To speed up the starting time, the MOC Server also resort on a binary dump, \nneeding synchronisation mechanisms with the running server data when the list of MOCs is updated. \n\n`moc-set` has primarily been developed for VizieR needs: lighter/simpler version of the MOC server, with \nless information needed (VizieR already store catalogues metadata), system programming language with no runtime, \npossibly less memory available, ...\n\n\n## Install\n\n### From pypi for python users\n\nMOCSet is available in [pypi](https://pypi.org/project/moc-set),\nyou can thus install the `mocset` executable using `pip`:\n```bash\npip install -U moc-set\nmocset --help\n```\n\n### Debian package\n\nDownload the last `mocset_vxx_yyy.deb` corresponding to your architecture\n(`x86_64_musl` has the most chances to fit your needs)\nfrom the [github release page](https://github.com/cds-astro/cds-moc-rust/releases).\n\nInstall the `.deb` by clicking on it or using the command line:\n```bash\nsudo dpkg -i mocset_vxx_yyy.deb\nsudo apt-get install -f\n```\n\nThen you can use the tool:\n```bash\nmocset\nman mocset\n```\n\nYou can uninstall using, e.g.:\n```bash\nsudo dpkg -r $(dpkg -f mocset_vxx_yyy.deb Package)\n```\n\n### Pre-compile binaries for MacOS, Linux and Windows\n\nDownload the last `mocset-vxx_yyy.tar.gz` corresponding to your architecture\nfrom the [github release page](https://github.com/cds-astro/cds-moc-rust/releases).\nYou probably want ot use:\n* Linux: `mocset-vxx-x86_64-unknown-linux-musl.tar.gz`\n* MacOS: `mocset-vxx-x86_64-apple-darwin.tar.gz`\n* Windows: `mocset-vxx-.zip`\n\nWARNING: for linux, use [`musl`](https://en.wikipedia.org/wiki/Musl) instead of `gnu` (high chances of incompatibility in the latter case)\n\nThe tar contains a single executable binary file.\n```bash\ntar xzvf mocset-vxx-yyy.tar.gz\n./mocset\n```\n\n### Compile from source code\n\n[Install rust](https://www.rust-lang.org/tools/install)\n(and check that `~/.cargo/bin/` is in your path),\nor update the Rust compiler with:\n```bash\nrustup update\n``` \n\nClone the [moc lib rust](https://github.com/cds-astro/cds-moc-rust) project:\n```dtd\ngit clone https://github.com/cds-astro/cds-moc-rust\n```\nInstall from using `cargo`:\n```bash\ncargo install --path crates/set\n```\nor\n```\nRUSTFLAGS='-C target-cpu=native' cargo install --path crates/set\n```\n\n## Usage\n\nExec `mocset --help` to get the help message:\n```\n> mocset --help\nCommand-line tool to build, update and query a persistent set of HEALPix Multi-Order Coverages maps (MOCs)\n\nUsage: mocset <COMMAND>\n\nCommands:\n make Make a new mocset\n append Append the given MOCs to an existing mocset\n chgstatus Change the status flag of the given MOCs identifiers (valid, deprecated, removed)\n purge Purge the mocset removing physically the MOCs flagged as 'removed'\n list Provide the list of the MOCs in the mocset and the associated flags\n query Query the mocset\n union Union of all MOCs in the moc-set matching a given region\n extract Extracts a MOC from the given moc-set\n help Print this message or the help of the given subcommand(s)\n\nOptions:\n -h, --help Print help\n -V, --version Print version\n```\n\n### MOC set creation\n\nSimply list in a csv file a set of identifier (integer in `[0, 281_474_976_710_655]`),\nand MOC FITS file path. See e.g the file [moclist.txt](resources/tests/moclist.txt):\n```bash\n1,data/CDS_B_bax_bax.fits\n2,data/CDS_I_172_irs.fits\n3,data/CDS_I_274_ccdm.fits\n4,data/CDS_I_42_catalog.fits\n5,data/CDS_II_203A_faint.fits\n6,data/CDS_II_261_GOODS_S.fits\n7,data/CDS_II_339_summary.fits\n8,data/CDS_II_97_ans.fits\n9,data/CDS_III_206_orion.fits\n10,data/CDS_III_43_main.fits\n...\n```\n\nThen execute `moc-set` from the `mocset` command:\n```bash\n> mocset make --n128 3 --moc-list moclist.txt --delimiter , mocset.bin\n```\nor from the source code, [installing](https://www.rust-lang.org/tools/install) the Rust compiler (including Cargo):\n```bash\n> cargo run --release -- make --n128 3 --moc-list moclist.txt --delimiter , mocset.bin\n```\nTo build the moc-set binary file `mocset.bin`.\n\nThe total number of MOCs that can be stored in the file equals `n128 * 128 - 1 (so 383 in the example above, since n128=3).\n\n\nSee the help message for more details:\n```\n> mocset make --help\nMake a new mocset\n\nUsage: mocset make [OPTIONS] <FILE>\n\nArguments:\n <FILE> Output file, storing the MOC set\n\nOptions:\n -l, --moc-list <FILE> Input file containing the 'moc_id moc_path' list (default: read from stdin) 'moc_id' must be a positive integer smaller than 281_474_976_710_655 (can be stored on 6 bytes). Use a negative value to flag as deprecated\n -d, --delimiter <SEPARATOR> Delimiter used to separate the moc identifier from the moc path [default: \" \"]\n -n, --n128 <N128> n x 128 - 1 = number of MOCs that can be stored in this moc set [default: 1]\n -h, --help Print help\n```\n\n### List the content of a MOC set\n\nSimply use `mocset list`:\n```\n> mocset list mocset.bin\nid,status,depth,n_ranges,byte_size\n1,valid,11,1673,13384\n2,valid,11,36022,288176\n3,valid,11,55470,443760\n4,valid,11,587,4696\n5,valid,11,534,4272\n6,valid,11,17,136\n...\n```\n* `status`: can be `valid`, `deprecated` or `removed`\n* `n_ranges`: number of ranges in the MOC\n* `byte_size`: size of the MOC stored in the MOC set (in bytes)\n\nSee the help message:\n```\n> mocset list --help\nProvide the list of the MOCs in the mocset and the associated flags\n\nUsage: mocset list [OPTIONS] <FILE>\n\nArguments:\n <FILE> The moc-set to be read\n\nOptions:\n -r, --ranges Print byte ranges instead of byte_size\n -h, --help Print help\n```\n\n\n### Querying a MOC set\n\nSee the help to get the different query modes:\n```\n> mocset query --help\nQuery the mocset\n\nUsage: mocset query [OPTIONS] <FILE> <COMMAND>\n\nCommands:\n pos Single position\n cone A cone, i.e. a position with a small area around (approximated by a MOC)\n moc The given MOC (you create a moc using moc-cli and pipe it into moc-set)\n help Print this message or the help of the given subcommand(s)\n\nArguments:\n <FILE> The moc-set to be read\n\nOptions:\n -d, --add-deprecated Also selects MOCs flagged as deprecated\n -c, --print-coverage Print in output the sky fraction (in '[0.0, 1.0]') covered by each selected MOC\n -p, --parallel <PARALLEL> Switch on multi-threading, with 'parallel' threads (made for SSD, not HDD)\n -h, --help Print help\n```\n\n#### Query for a single position\n\nTo obtain the list of the MOCs containing a the position 90.0 +0.0 (in decimal degrees), use:\n```bash\n> mocset query moclist.bin pos 90.0 +0.0\nid\n161\n```\nThe result is the list of the identifier of the MOC covering the input position (only one MOC, with identifier 161 in our example).\n\nSee the full help:\n```\n> mocset query pos --help\nSingle position\n\nUsage: mocset query <FILE> pos <LON_DEG> <LAT_DEG>\n\nArguments:\n <LON_DEG> Longitude of the cone center (in degrees)\n <LAT_DEG> Latitude of the cone center (in degrees)\n\nOptions:\n -h, --help Print help\n```\n\n\n#### Query for a cone\n\nTo obtain the list of the MOCs overlapping the cone of center 90.0 +0.0 and having a radius of 320 arcsec, use:\n```bash\n> mocset query mocset.bin cone 90.0 +0.0 320.0 --precision 5\nid\n2\n3\n35\n161\n```\n\n`--precision` is optional, its default value is 2:\n * at a `precision` of 0, `mocset` transforms the input cone in a MOC \ncontaining 1 to 9 values. \n * at a `precision` of 1, `mocset` transforms the input cone in a MOC\ncontaining 1 to `9x4` values.\n * at a `precision` of `n`, `mocset` transforms the input cone in a MOC\ncontaining 1 to `9x4^n` values.\n\nSee the help:\n```\n> mocset query cone --help\nA cone, i.e. a position with a small area around (approximated by a MOC)\n\nUsage: mocset query <FILE> cone [OPTIONS] <LON_DEG> <LAT_DEG> <R_ARCSEC>\n\nArguments:\n <LON_DEG> Longitude of the cone center (in degrees)\n <LAT_DEG> Latitude of the cone center (in degrees)\n <R_ARCSEC> Radius of the cone (in arcseconds)\n\nOptions:\n -p, --precision <PREC> MOC precision; 0: depth 'd' at which the cone is overlapped by 1 to max 9 cells; 1: depth 'd' + 1; n: depth 'd' + n [default: 2]\n -i, --included Returns MOCs containing the whole cone MOC (instead of overlapping only)\n -h, --help Print help\n```\n\n#### Query for a MOC\n\nTo obtain the list of the MOCs overlapping the MOC stored in a given FITs file, e.g the MOC of XMM4 DR9, use:\n```\n> mocset query mocset.bin moc YOUR_PATH/CDS_IX_59_xmm4dr9s.fits\nid\n1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n...\n```\n\nYou may also use a MOC generate on the fly using [moc-cli](https://github.com/cds-astro/cds-moc-rust/tree/main/crates/cli)\n```\n> moc from polygon 5 \"(0.0,0.0),(10.0,0.0),(0.0,10.0)\" ascii | mocset query mocset.bin moc - --format ascii\nid\n1\n2\n3\n4\n7\n8\n13\n26\n27\n35\n36\n60\n63\n...\n```\n\nSee the help\n```\n> mocset query moc --help\nThe given MOC (you create a moc using moc-cli and pipe it into moc-set)\n\nUsage: mocset query <FILE> moc [OPTIONS] <FILE>\n\nArguments:\n <FILE> Path of the input MOC file (or stdin if equals \"-\")\n\nOptions:\n -f, --format <INPUT_FMT> Format of the input MOC ('ascii', 'json' or 'fits') [default: guess from the file extension]\n -i, --included Returns MOCs containing the whole given MOC (instead of overlapping)\n -h, --help Print help\n```\n\n### Query from a STC-S region\n\nYou can query from a STC-S region using `moc-cli`:\n```bash\necho \"Intersection ICRS (\n Polygon 272.536719 -19.461249 272.542612 -19.476380 272.537389 -19.491509 272.540192 -19.499823\n 272.535455 -19.505218 272.528024 -19.505216 272.523437 -19.500298 272.514082 -19.503376 \n 272.502271 -19.500966 272.488647 -19.490390 272.481932 -19.490913 272.476737 -19.486589 \n 272.487633 -19.455645 272.500386 -19.444996 272.503003 -19.437557 272.512303 -19.432436 \n 272.514132 -19.423973 272.522103 -19.421523 272.524511 -19.413250 272.541021 -19.400024 \n 272.566264 -19.397500 272.564202 -19.389111 272.569055 -19.383210 272.588186 -19.386539 \n 272.593376 -19.381832 272.596327 -19.370541 272.624911 -19.358915 272.629256 -19.347842 \n 272.642277 -19.341020 272.651322 -19.330424 272.653174 -19.325079 272.648903 -19.313708 \n 272.639616 -19.311098 272.638128 -19.303083 272.632705 -19.299839 272.627971 -19.289408 \n 272.628226 -19.276293 272.633750 -19.270590 272.615109 -19.241810 272.614704 -19.221196 \n 272.618224 -19.215572 272.630809 -19.209945 272.633540 -19.198681 272.640711 -19.195292 \n 272.643028 -19.186751 272.651477 -19.182729 272.649821 -19.174859 272.656782 -19.169272 \n 272.658933 -19.161883 272.678012 -19.159481 272.689173 -19.176982 272.689395 -19.183512 \n 272.678006 -19.204016 272.671112 -19.206598 272.664854 -19.203523 272.662760 -19.211156 \n 272.654435 -19.214434 272.652969 -19.222085 272.656724 -19.242136 272.650071 -19.265092\n 272.652868 -19.274296 272.660871 -19.249462 272.670041 -19.247807 272.675533 -19.254935 \n 272.673291 -19.273917 272.668710 -19.279245 272.671460 -19.287043 272.667507 -19.293933\n 272.669261 -19.300601 272.663969 -19.307130 272.672626 -19.308954 272.675225 -19.316490\n 272.657188 -19.349105 272.657638 -19.367455 272.662447 -19.372035 272.662232 -19.378566\n 272.652479 -19.386871 272.645819 -19.387933 272.642279 -19.398277 272.629282 -19.402739\n 272.621487 -19.398197 272.611782 -19.405716 272.603367 -19.404667 272.586162 -19.422703\n 272.561792 -19.420008 272.555815 -19.413012 272.546500 -19.415611 272.537427 -19.424213\n 272.533081 -19.441402 \n Not (Polygon 272.511081 -19.487278 272.515300 -19.486595 272.517029 -19.471442 \n 272.511714 -19.458837 272.506430 -19.459001 272.496401 -19.474322 272.504821 -19.484924)\n Not (Polygon 272.630446 -19.234210 272.637274 -19.248542 272.638942 -19.231476 272.630868 -19.226364)\n)\" | moc from stcs 14 - ascii | mocset query mocset.bin moc - --format ascii\n```\n\n\n#### Generic parameter\n\nFor all queries, the option `--add-deprecated` (or `-d`) add the MOCs flagged as deprecated in\nthe output, e.g.:\n```bash\nmocset query --add-deprecated moclist.bin pos 90.0 +0.0 --precision 5\n```\n\n### Updating a MOC set\n\nYou can:\n* `chgstatus` change the status of a MOC in the MOC set to flag it as `deprecated` or back to `valid`, \n or as `removed` (WARNING: once removed, a MOC cannot be flagged back as `deprecated` or `valid`)\n* `append` a new MOC at the end of the MOC set, the ID of a removed MOC can be reused\n* `purge` a MOC set to physically remove all MOCs flagged as `removed`.\n This process basically re-write the whole MOC set file.\n \nExample of usage of `chgstatus`\n```\n> mocset list mocset.bin\nid,status,depth,n_ranges,byte_size\n1,valid,11,1673,13384\n2,valid,11,36022,288176\n...\n> mocset chgstatus mocset.bin 1 deprecated\n> mocset list mocset.bin\nid,status,depth,n_ranges,byte_size\n1,deprecated,11,1673,13384\n2,valid,11,36022,288176\n...\n> mocset chgstatus mocset.bin 1 valid\n> mocset list mocset.bin\nid,status,depth,n_ranges,byte_size\n1,valid,11,1673,13384\n2,valid,11,36022,288176\n...\n> mocset chgstatus mocset.bin 1 removed\n> mocset list mocset.bin\nid,status,depth,n_ranges,byte_size\n1,removed,11,1673,13384\n2,valid,11,36022,288176\n...\n```\n\nExample of usage of `append`:\n```\n> mocset append mocset.bin 3000 MY_PATH/my_new_moc.fits\n```\n\nExample of usage of `purge`:\n```\n> mocset purge mocset.bin\n```\n\nHelp messages:\n```\n> mocset chgstatus --help\nChange the status flag of the given MOCs identifiers (valid, deprecated, removed)\n\nUsage: mocset chgstatus <FILE> <NEW_STATUS> [IDS]...\n\nArguments:\n <FILE> The moc-set to be updated\n <NEW_STATUS> New status flag to be set\n [IDS]... Comma separated list of identifiers of the MOCs we want to modify the flag\n\nOptions:\n -h, --help Print help\n```\n\n```\n> mocset append --help\nAppend the given MOCs to an existing mocset\n\nUsage: mocset append <FILE> <ID> <MOC_PATH>\n\nArguments:\n <FILE> The moc-set to be updated\n <ID> Identifier of the MOC we want to append. 'moc_id' must be a positive integer smaller than 281_474_976_710_655 (can be stored on 6 bytes). Use a negative value to flag as deprecated\n <MOC_PATH> Path of the MOC to be append\n\nOptions:\n -h, --help Print help\n\n```\n\n\n```\n> mocset purge --help\nPurge the mocset removing physically the MOCs flagged as 'removed'\n\nUsage: mocset purge [OPTIONS] <FILE>\n\nArguments:\n <FILE> The moc-set file to be purge\n\nOptions:\n -n, --n128 <N128> n x 128 - 1 = number of MOCs that can be stored in this purged moc set, if larger than the current value\n -h, --help Print help\n```\n\n# Implementation information\n\n## Principle\n\nWe resort on mapped files and the system disk cache.\nAlthough the first `moc-set` query may still be quite long,\nthe performances of subsequent queries will depend on the ability\nof the system to keep the file's data in the disk cache.\n\n### Remark\n\nIf used on a server with a lot of I/O, the data may not stay in the disk cache for long.\nIf we nevertheless want to always answer quickly, there is at least three options:\n* write a daemon loading the full dataset in memory \n* create a VM (or a docker?) containing only the `moc-set` tool\n* my favourite one: use shared memory, resorting e.g. on the [shared_memory crate](https://crates.io/crates/shared_memory)\n\n### File structure\n\nThe structure of the file is made of two main blocks:\n* a fixed length header, made of\n + a fixed length metadata\n + a fixed length cumulative byte index\n* a extensible data part\n\n\n\n#### Metadata part\n\nA fixed size (chosen at creation) buffer of `n` `u64` elements.\n* the first `u64` contains an indication on the buffer size\n* all other `u64` values, one per MOC in the `moc-set`, are made of 3 components:\n + a `u8` flag taking 4 possible values (only 2 bits are used, 6 are remaining):\n - `Valid` MOC\n - `Deprecated` MOC\n - `Removed` MOC\n - `Free` slot\n + the depth of the MOC, stored on `u8 (max depth = 64, thus 2 bits are remaining and could be used)\n + the MOC identifier, stored on the 6 remaining bytes.\n\nWe stop reading the metadata when we encounter the first `Free` flag.\n\nThe file can store `n - 1` MOCs.\n\n#### Cumulative byte index\n\nA fixed size (chosen at creation) buffer of `n` `u64` elements.\n* the first `u64` contains the byte size of the header, i.e. the size of the file with no data\n it also correspond to the starting byte of the first MOC that will be inserted in the `moc-set`; \n* all other elements at index `i` contains the size of the file if only storing the \n $i+1$ first MOCs.\n\nTo get the size (in bytes) of the MOC at index `i`, we can simply perform the operation:\n`cumulIndex[i + 1] - cumulIndex[i]`.\n\n#### Data part\n\nA simple concatenation of the MOCs ranges. \nAccording to the depth of each MOC, the ranges are either ranges of `u32` or ranges of `u64`.\n\n\n\n\n### Updates and Reading while writing\n\nThe only MOC information that can be modified (re-written) is its status flag. \nBut the status flag is coded on a single byte and a CPU read and write single bytes atomically. \nAlthough, several cores may see the byte in a different state, it is not critical:\na MOC flagged as 'deprecated' or 'deleted' is still physically stored in the `moc-set`,\nand we can accept a small delay in changing its state.\n\n* Read operation order\n + do not need a read lock\n + read the metadata part of the header\n + read the cumulative bytes index in the header\n + read the MOC(s)\n* Write Operation order\n + ask for a write lock (create a .lock file)\n + append the new MOC(s) to the end of the file\n + append the new entries to the cumulative bytes index\n + possibly update the flag of existing MOCs and append new entries to the end of the header\n\nThe header, i.e. both the metadata and the cumulative byte index, is of fixed size,\nwith free space reserved at file creation. \nIf a problem occurs while writing, the update is simply going to be ignored\n(except the part written in the meta): at the next write operation, if the meta\nhas not been written (and it is the last part to be written), the code assumes\nthat the cumulative index beyond the know meta elements is free, the same for the\ndata byte beyond the last known cumulative index byte.\n\nIf a process is reading while another is writing, the newly written part will also\nsimply be ignored if the metadata part has not yet been updated/written.\n\nIt works well because we only append new MOCs (we never delete information), \nwe only update metadata to flag a MOC as removed of deprecated, and we\nrespect the read/write order as described above.\n\n#### Mocset file before adding a new MOC\n\n\n\n\n#### Add a new moc step 1/3\n\n\n\n\n#### add a new moc step 2/3\n\n\n\n\n#### add a new moc step 3/3\n\n\n\n\n#### Mocset file after having added a new MOC\n\n\n\n\n\n#### Purge\n\nThe purge operation is the only one removing physically stored MOCs. \nIt actually consists in building a new `moc-set`, removing the MOCs flagged as removed,\nin a temporary file, and then making a move replacing the previous `moc-set`\nby the new one. \nThe `purge` operation uses a write lock.\n\n\n## Recall\n\n* Drop linux disk cache, in root mode: `sync; echo 3 > /proc/sys/vm/drop_caches`\n* Build for being compatible with a large range of systems, avoiding the GLIBC version error\n (see [this post](https://stackoverflow.com/questions/63724484/build-and-bind-against-older-libc-version)):\n> cargo build --target x86_64-unknown-linux-musl\n\n",
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