Tracking changes
When you check out a Splitgraph image into a schema, sgr enables change
tracking via PostgreSQL audit triggers. When any application writes to that
schema, the audit triggers will capture the changes, allowing sgr to package
them into new images as a set of delta-compressed patches. This way, keeping
track of table history is space efficient.
You can view changes to the current working checkout or between any two images
in a repository with the sgr diff command.
You can view the history of all changes to an image with the
sgr log command. This shows just the
history following the parent chain of an image. Passing -t will make sgr
render the history of the whole repository as a tree.
Example
Let's create another example repository and give the new image a tag:
$ sgr example generate example/repo_2
$ sgr sql --schema example/repo_2 "SELECT * FROM demo ORDER BY key"
$ sgr tag example/repo_2 original_data
You can do the next step using any SQL client that can access the PostgreSQL
database backing the sgr engine, but sgr provides a shorthand to alter the
generated image:
$ sgr example alter example/repo_2
Deleting 2 rows...
Updating 2 rows...
Adding 2 rows...
Let's inspect the current state of the repository:
$ sgr sql --schema example/repo_2 "SELECT * FROM demo ORDER BY key"
You should see that the first two rows are now missing, the second two rows have been altered and two more rows have been added.
Let's compare the demo table to its previous version:
$ sgr diff example/repo_2 -v
Between 97900a827962 and the current working copy:
demo: added 4 rows, removed 4 rows.
- (0, '5feceb66ffc86f38d952786c6d696c79c2dbc239dd4e91b46729d73a27fb57e9')
- (1, '6b86b273ff34fce19d6b804eff5a3f5747ada4eaa22f1d49c01e52ddb7875b4b')
- (2, 'd4735e3a265e16eee03f59718b9b5d03019c07d8b6c51f90da3a666eec13ab35')
- (3, '4e07408562bedb8b60ce05c1decfe3ad16b72230967de01f640b7e4729b49fce')
+ (2, 'd4735e3a265e16eee03f59718b9b5d03019c07d8b6c51f90da3a666eec13ab35_UPDATED')
+ (3, '4e07408562bedb8b60ce05c1decfe3ad16b72230967de01f640b7e4729b49fce_UPDATED')
+ (10, '4a44dc15364204a80fe80e9039455cc1608281820fe2b24f1e5233ade6af1dd5')
+ (11, '4fc82b26aecb47d2868c4efbe3581732a3e7cbcc6c2efb32062c08170a05eeb8')
