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Writing data to Glean

This page describes the various ways in which data gets into Glean.

There are two main methods for creating a DB. Repo-wide indexing jobs which require multiple workers and have dependent tasks are managed by the server, while simple one-off DB creation can be performed independently by a single client.

Client-driven writing​

A database can be created by a client using any of these methods:

  1. Programmatically, using one of the APIs listed in APIs for Writing.
  2. On the command line: invoke the glean command-line tool to send data in JSON format, see Creating a database using the command line.
  3. In the shell, use glean shell --db-root=<dir> and then use the command :load to create a DB from a JSON file. See Loading a DB from JSON in the shell.

Server-driven writing​

Large indexing jobs are coordinated by the server, using a recipe to define the various tasks and the dependencies between them. Recipes are defined in the recipes configuration; see the --recipe-config option in Common options.

The job proceeds as follows:

  • An indexing job is started by calling the server's kickOff Thrift method. This creates a work queue of tasks on the server.

  • Clients obtain tasks from the server by calling getWork. Tasks may have dependencies between them, so the server won't hand out a task until its dependencies are complete.

  • When all tasks are done, the server marks the database as complete.

APIs for writing​

If none of the above work for you, the Thrift API enable basic write access to the database.

  • kickOff can be used to create a new DB
  • sendJsonBatch is for sending facts in JSON-serialized form
  • finishBatch exposes the result of a previously sent JSON batch
  • workFinished closes a DB

A rough outline of a client looks like:

glean = make_glean_thrift_client()
db_handle = make_uuid()
glean.kickOff(my_repo, KickOffFill(writeHandle=db_handle))
for json_batch in json_batches:
handle = glean.sendJsonBatch(json_batch)
result = glean.finishBatch(handle)
# handle result
glean.workFinished(my_repo, db_handle, success_or_failure)

Writing from the command line​

JSON format​

The JSON format for Glean data is described in Thrift and JSON.

Here's an example of JSON data for writing to Glean:

{ "predicate": "cxx1.Name.1", # define facts for cxx1.Name.1
"facts": [
{ "id": 1, "key": "abc" }, # define a fact with id 1
{ "id": 2, "key": "def" }
{ "predicate": "cxx1.FunctionName.1", # define facts for cxx1.FunctionName.1
"facts": [
{ "id": 3,
"key": {
"name": { "id": 1 }}} # reference to fact with id 1
{ "predicate": "cxx1.FunctionQName.1", # define facts for cxx1.FunctionQName.1
"facts": [
{ "key": {
"name": 3, # 3 is shorthand for { "id": 3 }
"scope": { "global_": {} } } },
{ "key": {
"name": {
"key": { # define a nested fact directly
"name": {
"key": "ghi" }}}, # another nested fact
"scope": {
"namespace_": {
"key": {
"name": {
"key": "std" }}}}}

The rules of the game are:

  • Predicate names must include versions, i.e. cxx1.Name.1 rather than cxx1.Name.
  • The id field when defining a fact is optional. The id numbers in the input file will not be the final id numbers assigned to the facts in the database.
  • There are no restrictions on id values (any 64-bit integer will do) but an id value may not be reused within a file.
  • Later facts may refer to earlier ones using either { "id": N } or just N.
  • It is only possible to refer to ids from facts in the same file, if you are writing multiple files using glean write or via the sendJsonBatch API.
  • a nested facts can be defined inline, instead of defining it with an id first and then referencing it.
  • an inline nested fact can be given an id and referred to later.

Loading a DB from JSON in the shell​

The shell is useful for experimenting with creating a DB from JSON data directly. Let's try loading the data above into a DB in the shell:

$ mkdir /tmp/glean
$ glean shell --db-root /tmp/glean
Glean Shell, dev mode
type :help for help.
no fbsource database availabe
> :load test/0 /home/smarlow/test
I0514 01:19:37.137109 3566745 Work.hs:184] test/16: database complete

Let's see what facts we loaded:

test> :stat
count: 72
size: 5988
count: 2
size: 66
count: 2
size: 70
count: 4
size: 148
count: 1
size: 35

Note that there were 4 cxx1.Name.1 facts - some of those were defined as inline nested facts in the JSON. We can query them all:

test> cxx1.Name _
4 results, 1 queries, 4 facts, 0.22ms, 44296 bytes

{ "id": 1096, "key": "abc" }
{ "id": 1097, "key": "def" }
{ "id": 1100, "key": "ghi" }
{ "id": 1102, "key": "std" }

Note that the id values here do not correspond to the id values in the input file.

Creating a database using the command line​

The glean command-line tool can be used to create a database directly on the server.

To create a database from a single file of JSON facts:

glean create --service <write-server> --finish --db <name>/<instance> <filename>


  • <write-server> is the host:port of the Glean server
  • <name> is the name for your DB. For indexing repositories we normally use the name of the repository, but it's just a string, so you can use whatever you want.
  • <hash> identifies this particular instance of your database. For repositories we normally use the revision hash, but, again, it's just a string.
  • <filename> the file containing the JSON facts.

If the file is more than, say, 100MB, this operation will probably time out sending the data to the server. To send large amounts of data you need to batch it up into multiple files, and then send it like this:

glean create --service <write-server> --db <name>/<hash>
glean write --service <write-server> --db <name>/<hash> <filename1>
glean write --service <write-server> --db <name>/<hash> <filename2>
glean finish --service <write-server> --db <name>/<hash>

To find out if your DB made it:

glean shell --service <write-server> :list

This will list the DBs available on the write server.