From 688b65ccde1579e247ad07a654b1c3e425ce5ca6 Mon Sep 17 00:00:00 2001
From: Julien Fontanet <julien.fontanet@isonoe.net>
Date: Tue, 26 Nov 2019 11:29:55 +0100
Subject: [PATCH] feat(xo-server/backups-ng): limit number of gc-ed deltas
 (#4674)

Merging multiple VHDs is currently a slow process which could be optimized by doing a single merge of a synthetic delta.

Until this is implement, the number of garbage collected deltas should be limited to avoid taking too much time (and possibly interrupted jobs) in case of an important retention change.
---
 CHANGELOG.unreleased.md                           |  1 +
 packages/xo-server/config.toml                    |  5 +++++
 .../xo-server/src/xo-mixins/backups-ng/index.js   | 15 +++++++++++++++
 3 files changed, 21 insertions(+)

diff --git a/CHANGELOG.unreleased.md b/CHANGELOG.unreleased.md
index ae89de3e4..3ce4b56d5 100644
--- a/CHANGELOG.unreleased.md
+++ b/CHANGELOG.unreleased.md
@@ -16,6 +16,7 @@
 
 - [Metadata backup] Add 10 minutes timeout to avoid stuck jobs [#4657](https://github.com/vatesfr/xen-orchestra/issues/4657) (PR [#4666](https://github.com/vatesfr/xen-orchestra/pull/4666))
 - [Metadata backups] Fix out-of-date listing for 1 minute due to cache (PR [#4672](https://github.com/vatesfr/xen-orchestra/pull/4672))
+- [Delta backup] Limit the number of merged deltas per run to avoid interrupted jobs (PR [#4674](https://github.com/vatesfr/xen-orchestra/pull/4674))
 
 ### Released packages
 
diff --git a/packages/xo-server/config.toml b/packages/xo-server/config.toml
index 4325fb34b..66db10465 100644
--- a/packages/xo-server/config.toml
+++ b/packages/xo-server/config.toml
@@ -67,6 +67,11 @@ poolMetadataTimeout = '10 minutes'
 #[http.helmet.hsts]
 #includeSubDomains = false
 
+# This is a work-around.
+#
+# See https://github.com/vatesfr/xen-orchestra/pull/4674
+maxMergedDeltasPerRun = 2
+
 [[http.listen]]
 port = 80
 
diff --git a/packages/xo-server/src/xo-mixins/backups-ng/index.js b/packages/xo-server/src/xo-mixins/backups-ng/index.js
index e07b27523..5745224e8 100644
--- a/packages/xo-server/src/xo-mixins/backups-ng/index.js
+++ b/packages/xo-server/src/xo-mixins/backups-ng/index.js
@@ -1594,6 +1594,21 @@ export default class BackupNg {
                   _ => _.mode === 'delta' && _.scheduleId === scheduleId
                 )
               ): any)
+
+              // FIXME: implement optimized multiple VHDs merging with synthetic
+              // delta
+              //
+              // For the time being, limit the number of deleted backups by run
+              // because it can take a very long time and can lead to
+              // interrupted backup with broken VHD chain.
+              //
+              // The old backups will be eventually merged in future runs of the
+              // job.
+              const { maxMergedDeltasPerRun } = this._backupOptions
+              if (oldBackups.length > maxMergedDeltasPerRun) {
+                oldBackups.length = maxMergedDeltasPerRun
+              }
+
               const deleteOldBackups = () =>
                 wrapTask(
                   {