85a0a6a28e
This change introduces a sync_store which holds only containers that are enabled for sync. The store is implemented using a directory structure that resembles that of the containers directory, but has entries only for containers enabled for sync. The store is maintained in two ways: 1. Preemptively by the container server when processing PUT/POST/DELETE operations targeted at containers with x-container-sync-key / x-container-sync-to 2. In the background using the containers replicator whenever it processes a container set up for sync The change updates [1] [1] http://docs.openstack.org/developer/swift/overview_container_sync.html Change-Id: I9ae4d4c7ff6336611df4122b7c753cc4fa46c0ff Closes-Bug: #1476623
483 lines
19 KiB
ReStructuredText
483 lines
19 KiB
ReStructuredText
======================================
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Container to Container Synchronization
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======================================
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--------
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Overview
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--------
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Swift has a feature where all the contents of a container can be mirrored to
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another container through background synchronization. Swift cluster operators
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configure their cluster to allow/accept sync requests to/from other clusters,
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and the user specifies where to sync their container to along with a secret
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synchronization key.
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.. note::
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Container sync will sync object POSTs only if the proxy server is set to
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use "object_post_as_copy = true" which is the default. So-called fast
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object posts, "object_post_as_copy = false" do not update the container
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listings and therefore can't be detected for synchronization.
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.. note::
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If you are using the large objects feature you will need to ensure both
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your manifest file and your segment files are synced if they happen to be
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in different containers.
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--------------------------
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Configuring Container Sync
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--------------------------
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Create a ``container-sync-realms.conf`` file specifying the allowable clusters
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and their information::
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[realm1]
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key = realm1key
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key2 = realm1key2
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cluster_clustername1 = https://host1/v1/
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cluster_clustername2 = https://host2/v1/
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[realm2]
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key = realm2key
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key2 = realm2key2
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cluster_clustername3 = https://host3/v1/
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cluster_clustername4 = https://host4/v1/
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Each section name is the name of a sync realm. A sync realm is a set of
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clusters that have agreed to allow container syncing with each other. Realm
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names will be considered case insensitive.
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The key is the overall cluster-to-cluster key used in combination with the
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external users' key that they set on their containers'
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``X-Container-Sync-Key`` metadata header values. These keys will be used to
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sign each request the container sync daemon makes and used to validate each
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incoming container sync request.
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The key2 is optional and is an additional key incoming requests will be checked
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against. This is so you can rotate keys if you wish; you move the existing key
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to key2 and make a new key value.
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Any values in the realm section whose names begin with ``cluster_`` will
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indicate the name and endpoint of a cluster and will be used by external users in
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their containers' ``X-Container-Sync-To`` metadata header values with the format
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"//realm_name/cluster_name/account_name/container_name". Realm and cluster
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names are considered case insensitive.
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The endpoint is what the container sync daemon will use when sending out
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requests to that cluster. Keep in mind this endpoint must be reachable by all
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container servers, since that is where the container sync daemon runs. Note
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that the endpoint ends with /v1/ and that the container sync daemon will then
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add the account/container/obj name after that.
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Distribute this ``container-sync-realms.conf`` file to all your proxy servers
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and container servers.
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You also need to add the container_sync middleware to your proxy pipeline. It
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needs to be after any memcache middleware and before any auth middleware. The
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container_sync section only needs the "use" item. For example::
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[pipeline:main]
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pipeline = healthcheck proxy-logging cache container_sync tempauth proxy-logging proxy-server
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[filter:container_sync]
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use = egg:swift#container_sync
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-------------------------------------------------------
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Old-Style: Configuring a Cluster's Allowable Sync Hosts
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-------------------------------------------------------
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This section is for the old-style of using container sync. See the previous
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section, Configuring Container Sync, for the new-style.
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With the old-style, the Swift cluster operator must allow synchronization with
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a set of hosts before the user can enable container synchronization. First, the
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backend container server needs to be given this list of hosts in the
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``container-server.conf`` file::
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[DEFAULT]
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# This is a comma separated list of hosts allowed in the
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# X-Container-Sync-To field for containers.
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# allowed_sync_hosts = 127.0.0.1
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allowed_sync_hosts = host1,host2,etc.
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...
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[container-sync]
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# You can override the default log routing for this app here (don't
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# use set!):
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# log_name = container-sync
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# log_facility = LOG_LOCAL0
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# log_level = INFO
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# Will sync, at most, each container once per interval
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# interval = 300
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# Maximum amount of time to spend syncing each container
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# container_time = 60
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----------------------
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Logging Container Sync
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----------------------
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Tracking sync progress, problems, and just general activity can only be
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achieved with log processing currently for container synchronization. In that
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light, you may wish to set the above `log_` options to direct the
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container-sync logs to a different file for easier monitoring. Additionally, it
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should be noted there is no way for an end user to detect sync progress or
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problems other than HEADing both containers and comparing the overall
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information.
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----------------------------------------------------------
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Using the ``swift`` tool to set up synchronized containers
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----------------------------------------------------------
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.. note::
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The ``swift`` tool is available from the `python-swiftclient`_ library.
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.. note::
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You must be the account admin on the account to set synchronization targets
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and keys.
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You simply tell each container where to sync to and give it a secret
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synchronization key. First, let's get the account details for our two cluster
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accounts::
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$ swift -A http://cluster1/auth/v1.0 -U test:tester -K testing stat -v
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StorageURL: http://cluster1/v1/AUTH_208d1854-e475-4500-b315-81de645d060e
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Auth Token: AUTH_tkd5359e46ff9e419fa193dbd367f3cd19
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Account: AUTH_208d1854-e475-4500-b315-81de645d060e
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Containers: 0
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Objects: 0
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Bytes: 0
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$ swift -A http://cluster2/auth/v1.0 -U test2:tester2 -K testing2 stat -v
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StorageURL: http://cluster2/v1/AUTH_33cdcad8-09fb-4940-90da-0f00cbf21c7c
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Auth Token: AUTH_tk816a1aaf403c49adb92ecfca2f88e430
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Account: AUTH_33cdcad8-09fb-4940-90da-0f00cbf21c7c
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Containers: 0
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Objects: 0
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Bytes: 0
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Now, let's make our first container and tell it to synchronize to a second
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we'll make next::
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$ swift -A http://cluster1/auth/v1.0 -U test:tester -K testing post \
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-t '//realm_name/clustername2/AUTH_33cdcad8-09fb-4940-90da-0f00cbf21c7c/container2' \
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-k 'secret' container1
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The ``-t`` indicates the cluster to sync to, which is the realm name of the
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section from container-sync-realms.conf, followed by the cluster name from
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that section (without the cluster\_ prefix), followed by the account and container
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names we want to sync to. The ``-k`` specifies the secret key the two containers will share for
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synchronization; this is the user key, the cluster key in
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container-sync-realms.conf will also be used behind the scenes.
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Now, we'll do something similar for the second cluster's container::
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$ swift -A http://cluster2/auth/v1.0 -U test2:tester2 -K testing2 post \
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-t '//realm_name/clustername1/AUTH_208d1854-e475-4500-b315-81de645d060e/container1' \
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-k 'secret' container2
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That's it. Now we can upload a bunch of stuff to the first container and watch
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as it gets synchronized over to the second::
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$ swift -A http://cluster1/auth/v1.0 -U test:tester -K testing \
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upload container1 .
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photo002.png
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photo004.png
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photo001.png
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photo003.png
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$ swift -A http://cluster2/auth/v1.0 -U test2:tester2 -K testing2 \
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list container2
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[Nothing there yet, so we wait a bit...]
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.. note::
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If you're an operator running SAIO and just testing, each time you
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configure a container for synchronization and place objects in the
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source container you will need to ensure that container-sync runs
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before attempting to retrieve objects from the target container.
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That is, you need to run::
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swift-init container-sync once
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Now expect to see objects copied from the first container to the second::
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$ swift -A http://cluster2/auth/v1.0 -U test2:tester2 -K testing2 \
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list container2
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photo001.png
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photo002.png
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photo003.png
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photo004.png
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You can also set up a chain of synced containers if you want more than two.
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You'd point 1 -> 2, then 2 -> 3, and finally 3 -> 1 for three containers.
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They'd all need to share the same secret synchronization key.
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.. _`python-swiftclient`: http://github.com/openstack/python-swiftclient
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-----------------------------------
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Using curl (or other tools) instead
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-----------------------------------
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So what's ``swift`` doing behind the scenes? Nothing overly complicated. It
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translates the ``-t <value>`` option into an ``X-Container-Sync-To: <value>``
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header and the ``-k <value>`` option into an ``X-Container-Sync-Key: <value>``
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header.
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For instance, when we created the first container above and told it to
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synchronize to the second, we could have used this curl command::
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$ curl -i -X POST -H 'X-Auth-Token: AUTH_tkd5359e46ff9e419fa193dbd367f3cd19' \
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-H 'X-Container-Sync-To: //realm_name/clustername2/AUTH_33cdcad8-09fb-4940-90da-0f00cbf21c7c/container2' \
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-H 'X-Container-Sync-Key: secret' \
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'http://cluster1/v1/AUTH_208d1854-e475-4500-b315-81de645d060e/container1'
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HTTP/1.1 204 No Content
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Content-Length: 0
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Content-Type: text/plain; charset=UTF-8
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Date: Thu, 24 Feb 2011 22:39:14 GMT
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---------------------------------------------------------------------
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Old-Style: Using the ``swift`` tool to set up synchronized containers
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---------------------------------------------------------------------
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.. note::
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The ``swift`` tool is available from the `python-swiftclient`_ library.
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.. note::
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You must be the account admin on the account to set synchronization targets
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and keys.
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This is for the old-style of container syncing using allowed_sync_hosts.
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You simply tell each container where to sync to and give it a secret
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synchronization key. First, let's get the account details for our two cluster
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accounts::
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$ swift -A http://cluster1/auth/v1.0 -U test:tester -K testing stat -v
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StorageURL: http://cluster1/v1/AUTH_208d1854-e475-4500-b315-81de645d060e
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Auth Token: AUTH_tkd5359e46ff9e419fa193dbd367f3cd19
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Account: AUTH_208d1854-e475-4500-b315-81de645d060e
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Containers: 0
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Objects: 0
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Bytes: 0
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$ swift -A http://cluster2/auth/v1.0 -U test2:tester2 -K testing2 stat -v
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StorageURL: http://cluster2/v1/AUTH_33cdcad8-09fb-4940-90da-0f00cbf21c7c
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Auth Token: AUTH_tk816a1aaf403c49adb92ecfca2f88e430
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Account: AUTH_33cdcad8-09fb-4940-90da-0f00cbf21c7c
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Containers: 0
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Objects: 0
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Bytes: 0
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Now, let's make our first container and tell it to synchronize to a second
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we'll make next::
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$ swift -A http://cluster1/auth/v1.0 -U test:tester -K testing post \
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-t 'http://cluster2/v1/AUTH_33cdcad8-09fb-4940-90da-0f00cbf21c7c/container2' \
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-k 'secret' container1
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The ``-t`` indicates the URL to sync to, which is the ``StorageURL`` from
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cluster2 we retrieved above plus the container name. The ``-k`` specifies the
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secret key the two containers will share for synchronization. Now, we'll do
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something similar for the second cluster's container::
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$ swift -A http://cluster2/auth/v1.0 -U test2:tester2 -K testing2 post \
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-t 'http://cluster1/v1/AUTH_208d1854-e475-4500-b315-81de645d060e/container1' \
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-k 'secret' container2
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That's it. Now we can upload a bunch of stuff to the first container and watch
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as it gets synchronized over to the second::
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$ swift -A http://cluster1/auth/v1.0 -U test:tester -K testing \
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upload container1 .
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photo002.png
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photo004.png
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photo001.png
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photo003.png
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$ swift -A http://cluster2/auth/v1.0 -U test2:tester2 -K testing2 \
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list container2
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[Nothing there yet, so we wait a bit...]
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[If you're an operator running SAIO and just testing, you may need to
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run 'swift-init container-sync once' to perform a sync scan.]
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$ swift -A http://cluster2/auth/v1.0 -U test2:tester2 -K testing2 \
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list container2
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photo001.png
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photo002.png
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photo003.png
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photo004.png
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You can also set up a chain of synced containers if you want more than two.
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You'd point 1 -> 2, then 2 -> 3, and finally 3 -> 1 for three containers.
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They'd all need to share the same secret synchronization key.
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.. _`python-swiftclient`: http://github.com/openstack/python-swiftclient
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----------------------------------------------
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Old-Style: Using curl (or other tools) instead
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----------------------------------------------
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This is for the old-style of container syncing using allowed_sync_hosts.
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|
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So what's ``swift`` doing behind the scenes? Nothing overly complicated. It
|
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translates the ``-t <value>`` option into an ``X-Container-Sync-To: <value>``
|
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header and the ``-k <value>`` option into an ``X-Container-Sync-Key: <value>``
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header.
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For instance, when we created the first container above and told it to
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synchronize to the second, we could have used this curl command::
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$ curl -i -X POST -H 'X-Auth-Token: AUTH_tkd5359e46ff9e419fa193dbd367f3cd19' \
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-H 'X-Container-Sync-To: http://cluster2/v1/AUTH_33cdcad8-09fb-4940-90da-0f00cbf21c7c/container2' \
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-H 'X-Container-Sync-Key: secret' \
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'http://cluster1/v1/AUTH_208d1854-e475-4500-b315-81de645d060e/container1'
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HTTP/1.1 204 No Content
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Content-Length: 0
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Content-Type: text/plain; charset=UTF-8
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Date: Thu, 24 Feb 2011 22:39:14 GMT
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--------------------------------------------------
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What's going on behind the scenes, in the cluster?
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--------------------------------------------------
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Container ring devices have a directory called ``containers``, where container
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databases reside. In addition to ``containers``, each container ring device
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also has a directory called ``sync-containers``. ``sync-containers`` holds
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symlinks to container databases that were configured for container sync using
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``x-container-sync-to`` and ``x-container-sync-key`` metadata keys.
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The swift-container-sync process does the job of sending updates to the remote
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container. This is done by scanning ``sync-containers`` for container
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databases. For each container db found, newer rows since the last sync will
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trigger PUTs or DELETEs to the other container.
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``sync-containers`` is maintained as follows:
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Whenever the container-server processes a PUT or a POST request that carries
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``x-container-sync-to`` and ``x-container-sync-key`` metadata keys the server
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creates a symlink to the container database in ``sync-containers``. Whenever
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the container server deletes a synced container, the appropriate symlink
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is deleted from ``sync-containers``.
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In addition to the container-server, the container-replicator process does the
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job of identifying containers that should be synchronized. This is done by
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scanning the local devices for container databases and checking for
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x-container-sync-to and x-container-sync-key metadata values. If they exist
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then a symlink to the container database is created in a sync-containers
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sub-directory on the same device.
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Similarly, when the container sync metadata keys are deleted, the container
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server and container-replicator would take care of deleting the symlinks
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from ``sync-containers``.
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.. note::
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The swift-container-sync process runs on each container server in the
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cluster and talks to the proxy servers (or load balancers) in the remote
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cluster. Therefore, the container servers must be permitted to initiate
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outbound connections to the remote proxy servers (or load balancers).
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.. note::
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Container sync will sync object POSTs only if the proxy server is set to
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use "object_post_as_copy = true" which is the default. So-called fast
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object posts, "object_post_as_copy = false" do not update the container
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listings and therefore can't be detected for synchronization.
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The actual syncing is slightly more complicated to make use of the three
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(or number-of-replicas) main nodes for a container without each trying to
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do the exact same work but also without missing work if one node happens to
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be down.
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Two sync points are kept in each container database. When syncing a
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container, the container-sync process figures out which replica of the
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container it has. In a standard 3-replica scenario, the process will
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have either replica number 0, 1, or 2. This is used to figure out
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which rows are belong to this sync process and which ones don't.
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An example may help. Assume a replica count of 3 and database row IDs
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are 1..6. Also, assume that container-sync is running on this
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container for the first time, hence SP1 = SP2 = -1. ::
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SP1
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SP2
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v
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-1 0 1 2 3 4 5 6
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First, the container-sync process looks for rows with id between SP1
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and SP2. Since this is the first run, SP1 = SP2 = -1, and there aren't
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any such rows. ::
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SP1
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SP2
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v
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-1 0 1 2 3 4 5 6
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Second, the container-sync process looks for rows with id greater than
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SP1, and syncs those rows which it owns. Ownership is based on the
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hash of the object name, so it's not always guaranteed to be exactly
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one out of every three rows, but it usually gets close. For the sake
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of example, let's say that this process ends up owning rows 2 and 5.
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Once it's finished trying to sync those rows, it updates SP1 to be the
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biggest row-id that it's seen, which is 6 in this example. ::
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SP2 SP1
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v v
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-1 0 1 2 3 4 5 6
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While all that was going on, clients uploaded new objects into the
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container, creating new rows in the database. ::
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SP2 SP1
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v v
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-1 0 1 2 3 4 5 6 7 8 9 10 11 12
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On the next run, the container-sync starts off looking at rows with
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ids between SP1 and SP2. This time, there are a bunch of them. The
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sync process try to sync all of them. If it succeeds, it will set
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SP2 to equal SP1. If it fails, it will set SP2 to the failed object
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and will continue to try all other objects till SP1, setting SP2 to
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the first object that failed.
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Under normal circumstances, the container-sync processes
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will have already taken care of synchronizing all rows, between SP1
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and SP2, resulting in a set of quick checks.
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However, if one of the sync
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processes failed for some reason, then this is a vital fallback to
|
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make sure all the objects in the container get synchronized. Without
|
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this seemingly-redundant work, any container-sync failure results in
|
|
unsynchronized objects. Note that the container sync will persistently
|
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retry to sync any faulty object until success, while logging each failure.
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|
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Once it's done with the fallback rows, and assuming no faults occurred,
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SP2 is advanced to SP1. ::
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SP2
|
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SP1
|
|
|
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|
v
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-1 0 1 2 3 4 5 6 7 8 9 10 11 12
|
|
|
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Then, rows with row ID greater than SP1 are synchronized (provided
|
|
this container-sync process is responsible for them), and SP1 is moved
|
|
up to the greatest row ID seen. ::
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|
|
|
SP2 SP1
|
|
| |
|
|
v v
|
|
-1 0 1 2 3 4 5 6 7 8 9 10 11 12
|