hive-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Sushanth Sowmyan (JIRA)" <>
Subject [jira] [Commented] (HIVE-12285) Add locking to HCatClient
Date Fri, 30 Oct 2015 16:50:28 GMT


Sushanth Sowmyan commented on HIVE-12285:

Agreed, HCatClient (& thus its HMSImpl) is a reasonable target for the locking functionality
being suggested. In general, a good way to think about this api point is that it is a slightly
higher level api that is intended to be public api, on top of things like IMetaStoreClient.
I do not think this will replace Driver - I think any query-based api would stick with Driver
(potentially dropping the direct ql Driver access and instead using the HS2 Driver, as Falcon
is already doing in some areas).

> Add locking to HCatClient
> -------------------------
>                 Key: HIVE-12285
>                 URL:
>             Project: Hive
>          Issue Type: Improvement
>          Components: HCatalog
>    Affects Versions: 2.0.0
>            Reporter: Elliot West
>            Assignee: Elliot West
>              Labels: concurrency, hcatalog, lock, locking, locks
> With the introduction of a concurrency model (HIVE-1293) Hive uses locks to coordinate
 access and updates to both table data and metadata. Within the Hive CLI such lock management
is seamless. However, Hive provides additional APIs that permit interaction with data repositories,
namely the HCatalog APIs. Currently, operations implemented by this API do not participate
with Hive's locking scheme. Furthermore, access to the locking mechanisms is not exposed by
the APIs (as is the case with the Metastore Thrift API) and so users are not able to explicitly
interact with locks either. This has created a less than ideal situation where users of the
APIs have no choice but to manipulate these data repositories outside of the command of Hive's
lock management, potentially resulting in situations where data inconsistencies can occur
both for external processes using the API and for queries executing within Hive.
> h3. Scope of work
> This ticket is concerned with sections of the HCatalog API that deal with DDL type operations
using the metastore, not with those whose purpose is to read/write table data. A separate
issue already exists for adding locking to HCat readers and writers (HIVE-6207).
> h3. Proposed work
> The following work items would serve as a minimum deliverable that would both allow API
users to effectively work with locks:
> * Comprehensively document on the wiki the locks required for various Hive operations.
At a minimum this should cover all operations exposed by {{HCatClient}}. The [Locking design
document|] can be used as a starting
point or perhaps updated.
> * Implement methods and types in the {{HCatClient}} API that allow users to manipulate
Hive locks. For the most part I'd expect these to delegate to the metastore API implementations:
> ** {{org.apache.hadoop.hive.metastore.IMetaStoreClient.lock(LockRequest)}}
> ** {{org.apache.hadoop.hive.metastore.IMetaStoreClient.checkLock(long)}}
> ** {{org.apache.hadoop.hive.metastore.IMetaStoreClient.unlock(long)}}
> ** -{{org.apache.hadoop.hive.metastore.IMetaStoreClient.showLocks()}}-
> ** {{org.apache.hadoop.hive.metastore.IMetaStoreClient.heartbeat(long, long)}}
> ** {{org.apache.hadoop.hive.metastore.api.LockComponent}}
> ** {{org.apache.hadoop.hive.metastore.api.LockRequest}}
> ** {{org.apache.hadoop.hive.metastore.api.LockResponse}}
> ** {{org.apache.hadoop.hive.metastore.api.LockLevel}}
> ** {{org.apache.hadoop.hive.metastore.api.LockType}}
> ** {{org.apache.hadoop.hive.metastore.api.LockState}}
> ** -{{org.apache.hadoop.hive.metastore.api.ShowLocksResponse}}-
> h3. Additional proposals
> Explicit lock management should be fairly simple to add to {{HCatClient}}, however it
puts the onus on the API user to correctly understand and implement code that uses lock in
an appropriate manner. Failure to do so may have undesirable consequences. With a simpler
user model the operations exposed on the API would automatically acquire and release the locks
that they need. This might work well for small numbers of operations, but not perhaps for
large sequences of invocations. (Do we need to worry about this though as the API methods
usually accept batches?).  Additionally tasks such as heartbeat management could also be handled
implicitly for long running sets of operations. With these concerns in mind it may also be
beneficial to deliver some of the following:
> * A means to automatically acquire/release appropriate locks for {{HCatClient}} operations.
> * A component that maintains a lock heartbeat from the client.
> * A strategy for switching between manual/automatic lock management, analogous to SQL's
{{autocommit}} for transactions.
> An API for lock and heartbeat management already exists in the HCatalog Mutation API
(see: {{org.apache.hive.hcatalog.streaming.mutate.client.lock}}). It will likely make sense
to refactor either this code and/or code that uses it.

This message was sent by Atlassian JIRA

View raw message