Jack and Ryan, one valid root at a time looks straightforward and good
enough for use cases like DR and certain table migration cases.
Here are questions for multiple valid roots at a time, which is needed by
federation use case, multiple storage tiers use case.
1. Metadata sync-up questions
1. Do we keep multiple sets of version files under different roots? I
assume yes because the table will be invalid if not when switching roots.
2. Do we sync-up all metadata files across roots? I assume we at
least need to sync version files, otherwise, it'd be better to consider
they are different tables.
3. How do we sync metadata to prevent any inconsistency?
2. Is there an alternative way to do that? Iceberg has a very nice
feature that each individual data file could be in any location, e.g.
regions or tiers. But, switching a root to read files from different
storage layers is not flexible, since the switching root applies to all
metadata files and data files of a table.
Best,
Yufei
On Sun, Aug 29, 2021 at 2:13 PM Jack Ye <yezhao...@gmail.com> wrote:
> trying to catch up with the conversation here, just typing some of my
> thought process:
>
> Based on my understanding, there are in general 2 use cases:
>
> 1. multiple data copies in different physical storages, which includes:
>
> 1.1 disaster recovery: if 1 storage is completely down, all access needs
> to be redirected another storage
> 1.2 multi-tier data access: a table is stored in multiple tiers, such as a
> fast single-availability-zone (AZ) layer, a common multi-AZ layer, and a
> slow but cheap archival layer
> 1.3 table migration: user can manually migrate a table to point to a
> completely different location with completely different set of data files
>
> 2. different access points referring to the same storage, which includes:
>
> 2.1 access point: different names are pointed to the same physical storage
> with different access policies.
>
>
> I think we mostly reached the consensus that multiple root locations are
> needed.
> Now we need to ask the question of "Can a user access the storage from
> catalog to at least get the table metadata and read all the different root
> locations".
> I think the answer is Yes for 1.2 and 1.3, but No for 1.1 and 2.1.
> Therefore, we need to deal with those 2 situations separately.
>
> For 1.1 and 2.1, the metadata cannot be accessed by the user unless an
> alternative root bucket/storage endpoint is provided at catalog level. So
> this information should be put as a part of the catalog API.
> For 1.2 and 1.3, we need some more details about the characteristics of
> the root location, specifically:
> 1. if the location is read only or it can also be written to. Typically we
> should only allow 1 single "master" write location to avoid complicated
> situations of data in different locations out of sync, unless certain
> storage supports a bi-directional sync.
> 2. how should a reader/writer choose which root to access. To achieve
> that, I think we need some root location resolver interface, with some
> implementations like RegionBasedRootLocationResolver,
> AccessPolicyBasedRootLocationResolver, etc. (this is just my brainstorming)
>
> -Jack Ye
>
>
>
>
>
>
> On Mon, Aug 23, 2021 at 4:06 PM Yufei Gu <flyrain...@gmail.com> wrote:
>
>> @Ryan, how do these properties work with multiple table locations?
>>
>> 1.
>>
>> write.metadata.path
>> 2.
>>
>> write.folder-storage.path
>> 3.
>>
>> write.object-storage.path
>>
>> The current logic with single table location is to honor these properties
>> on top of table location. In case of multiple roots(table locations), we
>> cannot mix them. For example, write.object-storage.path and table
>> location should be in the same region for the DR use case.
>>
>>
>> One of solutions to keep the similar logic is that we support all
>> properties for each root, like this
>>
>>
>> 1. Root1: (table location1, metadata path1, folder-storage path1,
>> object-storage path1)
>>
>> 2. Root2: (table location2, metadata path2, folder-storage path2,
>> object-storage path2)
>>
>> 3. Root3: (table location3, null, null, null)
>> What do you think?
>>
>> @Anjali, not sure supporting federation by using multiple roots is a good
>> idea. Can we create a partition with a specific location to distinguish
>> data between regions?
>>
>> On Mon, Aug 23, 2021 at 1:14 PM Anjali Norwood
>> <anorw...@netflix.com.invalid> wrote:
>>
>>> Hi Ryan, All,
>>>
>>> *"The more I think about this, the more I like the solution to add
>>> multiple table roots to metadata, rather than removing table roots. Adding
>>> a way to plug in a root selector makes a lot of sense to me and it ensures
>>> that the metadata is complete (table location is set in metadata) and that
>>> multiple locations can be used. Are there any objections or arguments
>>> against doing it that way?"*
>>>
>>> In the context of your comment on multiple locations above, I am
>>> thinking about the following scenarios:
>>> 1) Disaster recovery or low-latency use case where clients connect to
>>> the region geographically closest to them: In this case, multiple table
>>> roots represent a copy of the table, the copies may or may not be in sync.
>>> (Most likely active-active replication would be set up in this case and the
>>> copies are near-identical). A root level selector works/makes sense.
>>> 2) Data residency requirement: data must not leave a country/region. In
>>> this case, federation of data from multiple roots constitutes the entirety
>>> of the table.
>>> 3) One can also imagine combinations of 1 and 2 above where some
>>> locations need to be federated and some locations have data replicated from
>>> other locations.
>>>
>>> Curious how the 2nd and 3rd scenarios would be supported with this
>>> design.
>>>
>>> regards,
>>> Anjali.
>>>
>>>
>>>
>>> On Sun, Aug 22, 2021 at 11:22 PM Peter Vary <pv...@cloudera.com.invalid>
>>> wrote:
>>>
>>>>
>>>> @Ryan: If I understand correctly, currently there is a possibility to
>>>> change the root location of the table, and it will not change/move the old
>>>> data/metadata files created before the change, only the new data/metadata
>>>> files will be created in the new location.
>>>>
>>>> Are we planning to make sure that the tables with relative paths will
>>>> always contain every data/metadata file in single root folder?
>>>>
>>>> Here is a few scenarios which I am thinking about:
>>>> 1. Table T1 is created with relative path in HadoopCatalog/HiveCatalog
>>>> where the root location is L1, and this location is generated from the
>>>> TableIdentifier (at least in creation time)
>>>> 2. Data inserted to the table, so data files are created under L1, and
>>>> the metadata files contain R1 relative path to the current L1.
>>>> 3a. Table location is updated to L2 (Hive: ALTER TABLE T1 SET LOCATION
>>>> L2)
>>>> 3b. Table renamed to T2 (Hive: ALTER TABLE T1 RENAME TO T2) - Table
>>>> location is updated for Hive tables if the old location was the default
>>>> location.
>>>> 4. When we try to read this table we should read the old data/metadata
>>>> files as well.
>>>>
>>>> So in both cases we have to move the old data/metadata files around
>>>> like Hive does for the native tables, and for the tables with relative
>>>> paths we do not have to change the metadata other than the root path? Will
>>>> we do the same thing with other engines as well?
>>>>
>>>> Thanks,
>>>> Peter
>>>>
>>>> On Mon, 23 Aug 2021, 06:38 Yufei Gu, <flyrain...@gmail.com> wrote:
>>>>
>>>>> Steven, here is my understanding. It depends on whether you want to
>>>>> move the data. In the DR case, we do move the data, we expect data to be
>>>>> identical from time to time, but not always be. In the case of S3 aliases,
>>>>> different roots actually point to the same location, there is no data
>>>>> move,
>>>>> and data is identical for sure.
>>>>>
>>>>> On Sun, Aug 22, 2021 at 8:19 PM Steven Wu <stevenz...@gmail.com>
>>>>> wrote:
>>>>>
>>>>>> For the multiple table roots, do we expect or ensure that the data
>>>>>> are identical across the different roots? or this is best-effort
>>>>>> background
>>>>>> synchronization across the different roots?
>>>>>>
>>>>>> On Sun, Aug 22, 2021 at 11:53 AM Ryan Blue <b...@tabular.io> wrote:
>>>>>>
>>>>>>> Peter, I think that this feature would be useful when moving tables
>>>>>>> between root locations or when you want to maintain multiple root
>>>>>>> locations. Renames are orthogonal because a rename doesn't change the
>>>>>>> table
>>>>>>> location. You may want to move the table after a rename, and this would
>>>>>>> help in that case. But actually moving data is optional. That's why we
>>>>>>> put
>>>>>>> the table location in metadata.
>>>>>>>
>>>>>>> Anjali, DR is a big use case, but we also talked about directing
>>>>>>> accesses through other URLs, like S3 access points, table migration
>>>>>>> (like
>>>>>>> the rename case), and background data migration (e.g. lifting files
>>>>>>> between
>>>>>>> S3 regions). There are a few uses for it.
>>>>>>>
>>>>>>> The more I think about this, the more I like the solution to add
>>>>>>> multiple table roots to metadata, rather than removing table roots.
>>>>>>> Adding
>>>>>>> a way to plug in a root selector makes a lot of sense to me and it
>>>>>>> ensures
>>>>>>> that the metadata is complete (table location is set in metadata) and
>>>>>>> that
>>>>>>> multiple locations can be used. Are there any objections or arguments
>>>>>>> against doing it that way?
>>>>>>>
>>>>>>> On Fri, Aug 20, 2021 at 9:00 AM Anjali Norwood
>>>>>>> <anorw...@netflix.com.invalid> wrote:
>>>>>>>
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> This thread is about disaster recovery and relative paths, but I
>>>>>>>> wanted to ask an orthogonal but related question.
>>>>>>>> Do we see disaster recovery as the only (or main) use case for
>>>>>>>> multi-region?
>>>>>>>> Is data residency requirement a use case for anybody? Is it
>>>>>>>> possible to shard an iceberg table across regions? How is the location
>>>>>>>> managed in that case?
>>>>>>>>
>>>>>>>> thanks,
>>>>>>>> Anjali.
>>>>>>>>
>>>>>>>> On Fri, Aug 20, 2021 at 12:20 AM Peter Vary
>>>>>>>> <pv...@cloudera.com.invalid> wrote:
>>>>>>>>
>>>>>>>>> Sadly, I have missed the meeting :(
>>>>>>>>>
>>>>>>>>> Quick question:
>>>>>>>>> Was table rename / location change discussed for tables with
>>>>>>>>> relative paths?
>>>>>>>>>
>>>>>>>>> AFAIK when a table rename happens then we do not move old data /
>>>>>>>>> metadata files, we just change the root location of the new data /
>>>>>>>>> metadata
>>>>>>>>> files. If I am correct about this then we might need to handle this
>>>>>>>>> differently for tables with relative paths.
>>>>>>>>>
>>>>>>>>> Thanks, Peter
>>>>>>>>>
>>>>>>>>> On Fri, 13 Aug 2021, 15:12 Anjali Norwood,
>>>>>>>>> <anorw...@netflix.com.invalid> wrote:
>>>>>>>>>
>>>>>>>>>> Perfect, thank you Yufei.
>>>>>>>>>>
>>>>>>>>>> Regards
>>>>>>>>>> Anjali
>>>>>>>>>>
>>>>>>>>>> On Thu, Aug 12, 2021 at 9:58 PM Yufei Gu <flyrain...@gmail.com>
>>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>>> Hi Anjali,
>>>>>>>>>>>
>>>>>>>>>>> Inline...
>>>>>>>>>>> On Thu, Aug 12, 2021 at 5:31 PM Anjali Norwood
>>>>>>>>>>> <anorw...@netflix.com.invalid> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> Thanks for the summary Yufei.
>>>>>>>>>>>> Sorry, if this was already discussed, I missed the meeting
>>>>>>>>>>>> yesterday.
>>>>>>>>>>>> Is there anything in the design that would prevent multiple
>>>>>>>>>>>> roots from being in different aws regions?
>>>>>>>>>>>>
>>>>>>>>>>> No. DR is the major use case of relative paths, if not the only
>>>>>>>>>>> one. So, it will support roots in different regions.
>>>>>>>>>>>
>>>>>>>>>>> For disaster recovery in the case of an entire aws region down
>>>>>>>>>>>> or slow, is metastore still a point of failure or can metastore be
>>>>>>>>>>>> stood up
>>>>>>>>>>>> in a different region and could select a different root?
>>>>>>>>>>>>
>>>>>>>>>>> Normally, DR also requires a backup metastore, besides the
>>>>>>>>>>> storage(s3 bucket). In that case, the backup metastore will be in a
>>>>>>>>>>> different region along with the table files. For example, the
>>>>>>>>>>> primary table
>>>>>>>>>>> is located in region A as well as its metastore, the backup table is
>>>>>>>>>>> located in region B as well as its metastore. The primary table
>>>>>>>>>>> root points
>>>>>>>>>>> to a path in region A, while backup table root points to a path in
>>>>>>>>>>> region B.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>> regards,
>>>>>>>>>>>> Anjali.
>>>>>>>>>>>>
>>>>>>>>>>>> On Thu, Aug 12, 2021 at 11:35 AM Yufei Gu <flyrain...@gmail.com>
>>>>>>>>>>>> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> Here is a summary of yesterday's community sync-up.
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> Yufei gave a brief update on disaster recovery requirements
>>>>>>>>>>>>> and the current progress of relative path approach.
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> Ryan: We all agreed that relative path is the way for disaster
>>>>>>>>>>>>> recovery.
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> *Multiple roots for the relative path*
>>>>>>>>>>>>>
>>>>>>>>>>>>> Ryan proposed an idea to enable multiple roots for a table,
>>>>>>>>>>>>> basically, we can add a list of roots in table metadata, and use
>>>>>>>>>>>>> a selector
>>>>>>>>>>>>> to choose different roots when we move the table from one place
>>>>>>>>>>>>> to another.
>>>>>>>>>>>>> The selector reads a property to decide which root to use. The
>>>>>>>>>>>>> property
>>>>>>>>>>>>> could be either from catalog or the table metadata, which is yet
>>>>>>>>>>>>> to be
>>>>>>>>>>>>> decided.
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> Here is an example I’d image:
>>>>>>>>>>>>>
>>>>>>>>>>>>> 1. Root1: hdfs://nn:8020/path/to/the/table
>>>>>>>>>>>>> 2. Root2: s3://bucket1/path/to/the/table
>>>>>>>>>>>>> 3. Root3: s3://bucket2/path/to/the/table
>>>>>>>>>>>>>
>>>>>>>>>>>>> *Relative path use case*
>>>>>>>>>>>>>
>>>>>>>>>>>>> We brainstormed use cases for relative paths. Please let us
>>>>>>>>>>>>> know if there are any other use cases.
>>>>>>>>>>>>>
>>>>>>>>>>>>> 1. Disaster Recovery
>>>>>>>>>>>>> 2. Jack: AWS s3 bucket alias
>>>>>>>>>>>>> 3. Ryan: fall-back use case. In case that the root1
>>>>>>>>>>>>> doesn’t work, the table falls back to root2, then root3. As
>>>>>>>>>>>>> Russell
>>>>>>>>>>>>> mentioned, it is challenging to do snapshot expiration and
>>>>>>>>>>>>> other table
>>>>>>>>>>>>> maintenance actions.
>>>>>>>>>>>>>
>>>>>>>>>>>>> *Timeline*
>>>>>>>>>>>>>
>>>>>>>>>>>>> In terms of timeline, relative path could be a feature in Spec
>>>>>>>>>>>>> V3, since Spec V1 and V2 assume absolute path in metadata.
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> *Misc*
>>>>>>>>>>>>>
>>>>>>>>>>>>> 1. Miao: How is the relative path compatible with the
>>>>>>>>>>>>> absolute path?
>>>>>>>>>>>>> 2. How do we migrate an existing table? Build a tool for
>>>>>>>>>>>>> that.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Please let us know if you have any ideas, questions, or
>>>>>>>>>>>>> concerns.
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> Yufei
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> Ryan Blue
>>>>>>> Tabular
>>>>>>>
>>>>>>
