couchsnap

0.7.0 • Public • Published

couchsnap

Super-simple CouchDB snapshotting tool for creating incremental snapshots of the winning revisions of documents in a Apache CouchDB or Cloudant database.

  • winning revisions only of documents and design documents
  • no deletions (unless --deletions true is supplied).
  • no attachments
  • no conflicts

Installation

Install on your machine (Node.js & npm required):

$ npm install -g couchsnap

Reference

Environment variables:

  • COUCH_URL - the URL of your CouchDB service e.g. http://user:pass@myhost.com
  • COUCH_DATABASE - (optional) the name of the database to work with e.g. orders

Usage

  • --url/-u - same as COUCH_URL environment variable.
  • --database/-db/-d - same as `COUCH_DATABASE environment variable.
  • --deletions - include deleted documents in the output. (Default: false).

Put your CouchDB URL (with credentials) in an environment variable:

$ export COUCH_URL="https://username:password@mycouchdb.myhost.com"

Create a snapshot:

$ couchsnap --db mydb
spooling changes for mydb since 0
Finished fetching changes
mydb-snapshot-2022-11-09T16:04:06.195Z.jsonl
mydb-meta.json

At a later date, another snapshot can be taken:

$ couchsnap --db mydb
spooling changes for mydb since 23597-*****
mydb-snapshot-2022-11-09T16:04:51.041Z.jsonl
mydb-meta.json

Ad infinitum.

You may elect to include deleted documents by adding --deletions true e.g.

$ couchsnap --db mydb --deletions true
...

Finding a document's history

For a known document id e.g. abc123:

grep -h "abc123" mydb-snapshot-*

Restoring a database

Each backup file contains one document per line so we can feed this data to couchimport using its 'jsonl' mode. To ensure that we insert the newest data first, we can concatenate the snapshots in newest-first order:

# list the files in reverse time order, "cat" them and send them to couchimport
ls -t mydb-snapshot-* | xargs cat | couchimport --db mydb2 --type jsonl
# or use "tac" to reverse the order of each file
ls -t mydb-snapshot-* | xargs tac | couchimport --db mydb2 --type jsonl

Some caveats:

  1. This only restores to a new empty database.
  2. Deleted documents are neither backed-up nor restored (unless --deletions true is supplied).
  3. The restored documents will have a new _rev token. e.g. 1-abc123. i.e. the restored database would be unsuitable for a replicating relationship with the original database (as they have different revision histories).
  4. Attachments are neither backud-up or restored.
  5. Conflicting document revisions are neither backed-up nor restored.
  6. Secondary index definitions (in design documents) are backed up but will need to be rebuilt on restore.

How does it work?

couchsnap simply spools the changes feed storing the winning revisions of each non-deleted document to a file - one row line per document. The documents are stored without their revision tokens (_rev) to avoid creating conflicts on restore.

When snapshotting a database, two files are created:

<database>-snapshot-<timestamp>.jsonl
<database>-meta.json

The meta file contains meta data about where the last snapshot left off, so that a new snapshot can resume from the location.

Note: The nature of the CouchDB changes feed means that some snapshots may contain duplicate changes as the changes feed only guarantees "at least once" delivery.

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Install

npm i couchsnap

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Version

0.7.0

License

Apache-2.0

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  • glynnbird