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https://issues.apache.org/jira/browse/HBASE-798?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12620797#action_12620797
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Jonathan Gray commented on HBASE-798:
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I'm going to work on another patch now which adds a kind of "upsert/increment"
functionality. I have a few particular and frequent use cases in mind that
others may have a need for. Rough APIs below...
incrementColumnValue(table,row,family:column) -> Reads last value at column
(must be family:column), increments it, and writes new column version with
incremented value (wrapped in a single row lock for atomicity)
columnWithIncrementedValue(table,row,family,newcolumn) -> This may be more
limited to others, but we have many ordered column families where every column
value inserted is lexicographically smaller than all previous (always inserted
to the top). The value within each column is an incremented value. This grabs
the value of the top column in the family, increments it, and uses it as the
value for the newcolumn to be inserted at the top. There will be no checking
for newcolumn being smaller (lexicographically) than the last one, this is the
responsibility of the client, but this is assumed for correctness.
incrementColumn(table,row,family) -> This is also specialized. We assume a
schema where a family has only one column. We read that column value,
increment it, add the new column (reusing the old columns value), delete the
old column, release the lock, return the new incremented column to the client.
This is a way to provide a check-out mechanism for incrementing identifiers.
I'm going to build this patch on top of the previous patch because some helper
functions and classes will be useful.
> Provide Client API to explicitly lock and unlock rows
> -----------------------------------------------------
>
> Key: HBASE-798
> URL: https://issues.apache.org/jira/browse/HBASE-798
> Project: Hadoop HBase
> Issue Type: New Feature
> Components: client, ipc, regionserver
> Reporter: Jonathan Gray
> Priority: Minor
> Attachments: hbase-798-v1.patch
>
>
> We need to be able to perform a series of reads from and writes to a single
> row without any potential interference from other clients.
> Unfortunately this is a bit involved because normal reads currently do not
> acquire row locks, so it requires adding additional get/getRow calls that
> obtain and release a row lock.
> In addition, there will be two additional client calls, lockRow/unlockRow,
> which actually acquire and release the locks. Though each lock is associated
> with an HRegion, this will be tracked within the HRegionServer. When a lock
> is acquired from the client, it is handled much like a Scanner. We obtain
> the row lock from the HRegion, store the region name and lock identifier in a
> synchronized Map, and also obtain a lease to ensure that the lock will
> eventually be released even if the client dies.
> This also required adding a RowLockListener (implements LeaseListener)
> private class in HRS to handle row lock lease expiration.
> HRS.lockRow will return a long lockId (as openScanner does) that will be used
> in subsequent client calls to reuse this existing row lock. These calls will
> check that the lock is valid and perform the operations without any locking
> (wrappers around get*, new versions of batchUpdate, openScanner, etc).
> This is going to really add some noise to the list of available HTable/client
> methods so I'm not sure if it's something people would want to commit into a
> normal release. Regardless this does provide some very convenient
> functionality that may be useful to others.
> We are also looking into Clint Morgan's HBASE-669, but one major downside is
> that there is a significant amount of overhead involved. This row locking is
> already built in and this will only extend the API to allow clients to work
> with them directly. There is little to no overhead at all. The only
> (obvious) performance consideration is that this should only used where
> necessary as rows will not be locked and unlocked as quickly with round-trip
> client calls. In our design, we will have specific notes in our schema about
> which tables (or even which families or columns) must be accessed with row
> locks at all times and which do not.
> This is my first attempt at adding any additional functionality, so comments,
> criticism, code reviews are encouraged.
> I should have a patch up tomorrow.
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