backupccl: OOM while restoring backup in 22.2

[renatolabs]

While working on a roachtest (#103228), I saw a RESTORE fail because a couple of nodes went OOM. The backup was taken using the following command:

BACKUP INTO 'gs://cockroachdb-backup-testing/9_22.2.9-to-current_cluster_all-planned-and-executed-on-random-node_X4iV?AUTH=implicit' AS OF SYSTEM TIME '1684255935229011892.0000000000' WITH detached, encryption_passphrase = 'kvxN1Tmlwg0OesQw86rg8xjhsQdKBdHFZ7'

Worth noting about this backup (may or may not be relevant):

• it was taken while the cluster was in mixed-version state.
• an incremental backup was taken shortly (30s) after the full backup finished (for full logs, see [1]).
• both jobs were paused and resumed a couple of times while they ran.
• the backup does not include revision_history.

At a certain point in the test, we attempt to restore this backup on a 4-node cluster on v22.2.9. This failed because two of the nodes went OOM a few minutes after the RESTORE statement:

This backup does not contain a lot of data. The biggest table has ~2GiB of data in it:

$ ./cockroach sql --insecure -e "SELECT database_name, parent_schema_name, object_name, size_bytes FROM [SHOW BACKUP LATEST IN 'gs://cockroach-tmp/backup_issue_22_2_oom/9_22.2.9-to-current_cluster_all-planned-and-executed-on-random-node_X4iV?AUTH=implicit' WITH check_files, encryption_passphrase = 'kvxN1Tmlwg0OesQw86rg8xjhsQdKBdHFZ7'] ORDER BY size_bytes DESC LIMIT 5"
database_name   parent_schema_name      object_name     size_bytes
tpcc    public  stock   3217512461
tpcc    public  order_line      1858665525
tpcc    public  customer        1848283823
bank    public  bank    1310901452
restore_1_22_2_9_to_current_database_bank_before_upgrade_in_22_2_9_1    public  bank    1310899634

More importantly, very similar backups in other tests can be successfully restored in 22.2, so I think something went wrong with this particular backup.

Reproduction

The issue can be very easily reproduced by attempting to restore this backup on a 22.2 cluster (I have since moved the backup to a bucket with longer TTL [2]). This happens even on a completely empty cluster, with no workloads running.

The commands below will create a node with 14GiB of memory, just like the nodes in the failed test.

$ roachprod create -n 1 $CLUSTER
$ roachprod stage $CLUSTER release v22.2.9
$ roachprod start $CLUSTER
$ roachprod ssh $CLUSTER
...
ubuntu@CLUSTER $ time ./cockroach sql --insecure -e "RESTORE FROM LATEST IN 'gs://cockroach-tmp/backup_issue_22_2_oom/9_22.2.9-to-current_cluster_all-planned-and-executed-on-random-node_X4iV?AUTH=implicit' WITH encryption_passphrase = 'kvxN1Tmlwg0OesQw86rg8xjhsQdKBdHFZ7';"
ERROR: connection lost.

ERROR: -e: unexpected EOF
Failed running "sql"

real    2m46.609s
user    0m0.623s
sys     0m0.280s

Finally, note that this does not happen on master or 23.1.1.

[1] roachtest artifacts
[2] 9_22.2.9-to-current_cluster_all-planned-and-executed-on-random-node_X4iV

Jira issue: CRDB-28023

[blathers-crl]

cc @cockroachdb/disaster-recovery

[msbutler]

Nice Repro!

Here's what the heap looks like before the OOM. Looks like the http client is buffering too much data for some reason. Digging further.

[msbutler]

Looks like golang's http2 package is ooming. I suppose this OOM is not occurring on later releases because they use newer versions of go.

[dt]

because they use newer versions of go.

I'd be a little surprised if we'd be seeing a stdlib leak; seems more likely this is us just not sending as much over an http2-backed RPC (e.g. gRPC)

[msbutler]

Summarizing chatter over slack thread:

The http client is ooming, and either of the following patches prevents an oom, at least in the repro above:

1. Cherry pick backupccl: move openSSTs call into the restore workers #98906, which reduces the memory overhead of keeping open a bunch of large files. With this patch, we close files more eagerly. It could be worth backporting this.
2. Updating golang.org/x/net to 0.8.0, which contains a patch of x/net/http2: Memory leak regression introduced in window updates change golang/go#56315.

One unsatisfying note is that even after applying either patch, memory consumption seems to remain dangerously high, around 12 GiB in this repro. So, a backport of either patch could be a bandaid, but if we restore a longer chain even with the patches, we may still oom.

The ultimate solution is to include memory monitoring in the restore data processor (#93324), but that's not backportable.

I believe the only further action items are to consider the above backports to 22.2 (i.e. more testing).

[shermanCRL]

Cherry pick #98906, which reduces the memory overhead of keeping open a bunch of large files. With this patch, we close files more eagerly. It could be worth backporting this.

Should it just be a typical series of backports instead of a cherry pick? Do v23.1 first, then v22.2?

[msbutler]

#98906 is already in 23.1

[shermanCRL]

(Previous question deleted, nm, I was reading wrong.)