How does the Replication Log and Replication Log History work? [#2947873]

Hi,

I am trying to understand how the replication log and replication log history work. And what the relationship is between:
replication
replication_log
replication__log_history

I am trying to do a deploy to multiple remote workspaces using a custom module. The first workspace gets deployed OK but the second always hangs with the following messages printed in the nginx error log:

2018/02/26 07:30:27 [info] 27451#27451: *122 epoll_wait() reported that client prematurely closed connection, so upstream connection is closed too while sending request to upstream, client: 192.168.56.102, server: drupalvm.test, request: "GET /relaxed/live/_changes?feed=normal&style=all_docs&since=0&filter=published&parameters%5Binclude_unpublishable_entities%5D=0&limit=1000 HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "drupalvm.test"

I am assuming (and please let me know if I am wrong that it's because of that since=0. Changing any of the other replication settings including setting limit to 10 does not make a difference. What is the since for? Is since=0 basically telling the replicator to check for changes since the beginning of "time"?

Is it normal for a site with 124replication entries (attempted deploys) to have only 12 replication_log entries but 512 replication_log_revision and replication_log_history entries?

Thanks for any light you may be able to shed on this.

Comments

Comment #1

26 February 2018 at 10:02

pavlosdan created an issue. See original summary.

Comment #2

jeqq commented 13 March 2018 at 12:41

@pavlosdan I'll try to answer all your questions.

since - This parameter is used to indicate the start sequence for replication. Each entity has assigned a sequence in the key value storage (as I remember it's equal with the timestamp when the entry was created in key value storage). If since is 0 then the replicator will look for all changes starting from the beginning (from the first entity).

limit - Will limit the number of returned changes.

replication table - Contains information about the Replication entity type, about a deployment. A replication entity is created on each new deployment.

replication_log, replication_log_revision, replication_log_history - Tables for the Replication Log entity type.

It's normal to have 124 replications, 12 replication logs and 512 replication logs revisions.

Why? - because you have created 124 new deployments (when redeploying the same deployment there will just be created a new revision_log revision, not a new replication entity and not a new replication_log entity).

Replication logs are created one entity per source + target couple (for replication from live to stage and vice versa you will have 2 replication logs).

Having multiple replication logs is obvious, on each replication (deployment) you can have new revisions for the same replication_log entity.