It's the last commit of https://github.com/stoty/hbase/tree/PHOENIX_DUMMY_CELL_WORKAROUND It should be publicly accessible.
https://github.com/stoty/hbase/commit/fc47ffd8c86c0e104bbd29f01ed023690cdb93d3 is the commit. Phoenix trunk does some incrementing/decrementing the dummy rowkey. I have changed that to always return the processed rowkey, which has fixed some of the failing tests, but broke others, because the dummy key was now interpreted as processed, which caused HBase to skip the row on retry. Without the Phoenix side change (linked in an earlier mail), even more (but different) region split/move tests failed with HBase 3. On Tue, Nov 25, 2025 at 8:43 AM Viraj Jasani <[email protected]> wrote: > Istvan, > > > > I had to add this hack to get some tests in Phoenix to pass: > https://github.com/stoty/hbase/tree/PHOENIX_DUMMY_CELL_WORKAROUND > > Could you please share the git commit that has hack? > > We had bit more discussion internally and we are still not clear on what is > the exact root cause i.e. how cursor/heartbeat collides with dummy rowkey > only for hbase 3 and not for hbase 2. > > > On Fri, Nov 21, 2025 at 1:34 PM Istvan Toth <[email protected]> wrote: > > > That doesn't help us with the timeout setting. > > > > My plan is to remove the time field and logic from PhoenixScannerContext > > and rely on the existing one in ScannerContext as the heartbeat logic > uses > > that one. > > > > The lack of setter is not a show stopper, I'm pretty sure we can set that > > via reflection if all else fails. > > > > Istvan > > > > > > On Fri, Nov 21, 2025 at 8:04 AM Tanuj Khurana <[email protected]> > wrote: > > > > > Hi Istvan, > > > > > > As part of PHOENIX-7707, Phoenix extends the ScannerContext so that we > > can > > > add custom fields to it. > > > > > > On Fri, 21 Nov 2025 at 10:53, Istvan Toth <[email protected]> wrote: > > > > > > > Thanks for these points, Kadir. > > > > > > > > On Thu, Nov 20, 2025 at 8:59 PM Kadir Ozdemir < > > > > [email protected]> > > > > wrote: > > > > > > > > > The row key of the dummy result is not simply the last row that was > > > > scanned > > > > > by RegionScannerImpl. It is computed by Phoenix coprocs based on > the > > > > query. > > > > > For example, for an ordered group by query, it should be the last > row > > > of > > > > > the last group computed. For an unordered group by query, it nevers > > > > changes > > > > > until the entire region is processed. For Phoenix to be able to > use > > > the > > > > > HBase cursor, the coprocs needs to be able to change the cursor > > value. > > > > > Otherwise, there will be data integrity issues. > > > > > > > > > > > > > We can create a new synthetic Cursor Result and return that the same > > way > > > we > > > > create and return a new dummy Cell now. > > > > In this regard I see no difference between the two. > > > > > > > > > > > > > > > > > > Another reason for the dummy result is to provide an end-to-end > fair > > > > > scheduling for Phoenix in future. Without a Phoenix level signal > (the > > > > dummy > > > > > result), the Phoenix client would not know if the server already > > spent > > > > the > > > > > page time for a given query. I was thinking that we may be able to > > > > leverage > > > > > this to decide if the current blocked thread should be released. > This > > > is > > > > a > > > > > secondary concern but I want to make sure we all understand the > > > > > implications of replacing this Phoenix level concept. > > > > > > > > > > > > > Good point. > > > > > > > > My current understanding is that if we set the *needCursorResult* > flag > > on > > > > the scan, > > > > then HBase will return all cursor results to the client, and we can > use > > > > those the same way > > > > we use the dummy cells, so I see no problem here either. > > > > > > > > In fact the more I look the Hbase Heartbeat/cursor implementation, > the > > > more > > > > it feels like it was > > > > taylor made for implementing Phoenix paging (even though it was not > > > coming > > > > from Phoenix developers) > > > > > > > > The only snag I've found so far is that HBase creates the default > > > > ScannerContext and there is no easy way > > > > to set a custom paging time on it. > > > > > > > > > > > > > On Wed, Nov 19, 2025 at 9:27 PM Istvan Toth > > <[email protected] > > > > > > > > > wrote: > > > > > > > > > > > I'm glad that you as the original designer of the feature has > > joined > > > > the > > > > > > discussion, Kadir. > > > > > > > > > > > > On Wed, Nov 19, 2025 at 10:56 PM Kadir Ozdemir <[email protected] > > > > > > wrote: > > > > > > > > > > > > > Istvan, > > > > > > > > > > > > > > When I introduced server paging and the dummy result, Phoenix > did > > > not > > > > > > > support ScannerContext. Now that Phoenix supports > ScannerContext, > > > we > > > > > can > > > > > > > think about leveraging it better for server paging. > > > > > > > > > > > > > > > > > > > I realize that it was necessary for HBase 1.x. This was a good > > design > > > > > when > > > > > > HBase 1 > > > > > > support was a requirement, but specifically the dummy cell > > > > implementation > > > > > > detail > > > > > > is redundant now that HBase 2+ has native support for the same > > > > > > functionality. > > > > > > > > > > > > > > > > > > > > > > > > > > "HBase is not aware that these are dummy cells, and is > > considering > > > > the > > > > > > rows > > > > > > > as already processed when retrying scans after the region goes > > away > > > > > from > > > > > > > under the scan, i.e. it restarts the scan from AFTER the dummy > > > cell's > > > > > > > rowkey, leading to the scan skipping rows." > > > > > > > > > > > > > > > > > > > This assumption is no longer true in HBase 3. > > > > > > > > > > > > The client side heartbeat logic in HBase 3 is thrown off by the > > dummy > > > > > cells > > > > > > generated by Phoenix. > > > > > > > > > > > > I had to add this hack to get some tests in Phoenix to pass: > > > > > > > https://github.com/stoty/hbase/tree/PHOENIX_DUMMY_CELL_WORKAROUND > > > > > > > > > > > > > > > > > > > > > > > > > > That is the whole purpose of the dummy result, that is, not to > > scan > > > > the > > > > > > > rows that have been scanned already. This allows Phoenix to > make > > > > > progress > > > > > > > in the presence of table region movements, otherwise every > time a > > > > > region > > > > > > > moves or splits, Phoenix has to scan the region from the row > key > > of > > > > the > > > > > > > last valid result from this region instead of the last scanned > > row. > > > > > What > > > > > > is > > > > > > > the problem with this? Consider a large region and a scan with > a > > > very > > > > > > > selective filter such that a large number of rows need to be > > > scanned > > > > > > before > > > > > > > returning a valid row. One can create a sequence of region > > > movements > > > > > that > > > > > > > prevents Phoenix from making any progress for this scan > > > > > > > > > > > > > > > > > > Thanks for the explanation. > > > > > > > > > > > > I'm not questioning the usefulness of the paging design. > > > > > > The HBase community also agrees, so they have added this feature > > > > natively > > > > > > in > > > > > > HBase 2 in the form of the heartbeat/cursor feature. > > > > > > > > > > > > . > > > > > > > > > > > > > > Please note that Phoenix has some complex logic on the server > > side > > > > for > > > > > > > handling various SQL language features including grouping, > > > > aggregating, > > > > > > > sorting and joining. Implementing paging is much more complex > in > > > > > Phoenix > > > > > > > than implementing keep alive and ScannerContext in HBase. > Either > > > you > > > > > > > discovered an issue in Phoenix paging or a compatibility issue > > > > between > > > > > > > HBase 2 and HBase 3. I suggest that we understand what the > issue > > is > > > > > first > > > > > > > before replacing the dummy result. > > > > > > > > > > > > > > > > > > > It is the latter. > > > > > > > > > > > > The internal heartbeat retry logic in the HBase 3 client sees the > > > dummy > > > > > row > > > > > > and concludes that > > > > > > it should continue after an error (i.e. region move) from AFTER > > that > > > > row. > > > > > > (see my HBase hack above) > > > > > > > > > > > > This is different from the HBase 2 logic, which does not do this. > > > > > > > > > > > > In a way, this is related to, and sometimes casued by another > > Phoenix > > > > > > change I have made for HBase 3: > > > > > > PHOENIX-7728 <https://issues.apache.org/jira/browse/PHOENIX-7728 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://github.com/stoty/phoenix/blob/62112097bc1f050a760225663001fc0f084d4fb4/phoenix-core-server/src/main/java/org/apache/phoenix/coprocessor/GroupedAggregateRegionObserver.java#L482 > > > > > > <https://issues.apache.org/jira/browse/PHOENIX-7728> > > > > > > > > > > > > However, without removing the plus/minus row logic there even > more > > > > tests > > > > > > were failing, so > > > > > > Hbase 3 doesn't work with the current Phoenix dummy row logic > > either. > > > > > > > > > > > > <https://issues.apache.org/jira/browse/PHOENIX-7728>I agree that > > > > Phoenix > > > > > > still needs to be aware of paging, and will need logic to convert > > the > > > > > > Cursor rowkeys returned from inner scanners into rowkeys that > make > > > > sense > > > > > > for the outer scanners and client, but > > > > > > my expectation is that we can simply? convert the current Dummy > > cell > > > > > logic > > > > > > that handles this to work with the > > > > > > cursor value instead on the server side. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Wed, Nov 19, 2025 at 7:23 AM Tanuj Khurana < > > [email protected] > > > > > > > > > > wrote: > > > > > > > > > > > > > > > Hi Istvan, > > > > > > > > > > > > > > > > I agree that instead of using dummy cells, we should rely on > > > > > > > > keepalive/cursor mechanics. We have been working towards > that. > > As > > > > > part > > > > > > of > > > > > > > > PHOENIX-7707, I propagated the scanner context all the way > > down > > > to > > > > > > > phoenix > > > > > > > > scanners. We can leverage that. > > > > > > > > > > > > > > > > Tanuj > > > > > > > > > > > > > > > > On Wed, 19 Nov 2025 at 20:09, Istvan Toth > > > > <[email protected] > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > Thanks for your thoughtful response, Viraj. > > > > > > > > > > > > > > > > > > I have added my thoughts below. > > > > > > > > > > > > > > > > > > On Wed, Nov 19, 2025 at 2:38 PM Viraj Jasani < > > > [email protected] > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > We also need to understand: what happens when hbase > client > > > gets > > > > > > > > heartbeat > > > > > > > > > > and the region moves? > > > > > > > > > > > > > > > > > > > > I have checked that code in HBase, and the HBase client > > seems > > > > to > > > > > > > handle > > > > > > > > > this case transparently. > > > > > > > > > We may of course find bugs, but handling that is part of > the > > > > > design. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Wed, Nov 19, 2025 at 7:05 PM Viraj Jasani < > > > > [email protected] > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > Istvan, I think we should also involve dev@hbase and > see > > > > what > > > > > > > > > guidelines > > > > > > > > > > > we are recommending so far for coprocs that would like > to > > > > > > implement > > > > > > > > > > timeout > > > > > > > > > > > features for long running scans, wdyt? > > > > > > > > > > > > > > > > > > > > > > > > > > > > Based on my current understanding, if the Scan / > > ScannerContext > > > > is > > > > > > > > > correctly set up (allows partial rows, sets the time limit > > and > > > > > > > requests a > > > > > > > > > cursor), > > > > > > > > > HBase will honor that and the Scan will return a heartbeat > > > result > > > > > > when > > > > > > > it > > > > > > > > > times out. > > > > > > > > > > > > > > > > > > I THINK that's all we need. Of course if we get stuck we > > should > > > > ask > > > > > > for > > > > > > > > > help. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Wed, Nov 19, 2025 at 6:51 PM Viraj Jasani < > > > > > [email protected] > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > >> Thank you for starting this thread, Istvan! > > > > > > > > > > >> > > > > > > > > > > >> This is an important issue. I have recently come > across > > > data > > > > > > > > > correctness > > > > > > > > > > >> issues with PHOENIX-7733, to be fixed by HBASE-29722. > > This > > > > > also > > > > > > > got > > > > > > > > me > > > > > > > > > > >> thinking about the heartbeat and dummy cell overlap > > > leading > > > > to > > > > > > > > > possible > > > > > > > > > > >> data correctness issues. > > > > > > > > > > >> > > > > > > > > > > >> > I propose dropping the dummy cell mechanics from > > > Phoenix, > > > > > and > > > > > > > > using > > > > > > > > > > the > > > > > > > > > > >> > HBase keepalive/cursor mechanics instead (we may not > > > even > > > > > need > > > > > > > the > > > > > > > > > > >> cursors). > > > > > > > > > > >> > > > > > > > > > > >> +1 > > > > > > > > > > >> > > > > > > > > > > >> > If we cannot find a better way to shortcut some > > > processing > > > > > in > > > > > > > > > Phoenix > > > > > > > > > > we > > > > > > > > > > >> > may need to keep dummy cells internally, but we have > > to > > > > make > > > > > > > sure > > > > > > > > > that > > > > > > > > > > >> they > > > > > > > > > > >> > never appear on the wire and reach the client. > > > > > > > > > > >> > > > > > > > > > > >> I don't think it is possible for Phoenix to ensure a > > dummy > > > > > cell > > > > > > > > never > > > > > > > > > > >> reaches the HBase client. > > > > > > > > > > > > > > > > > > > > > > > > > > > > I think if nothing else works, we can still catch and > > > > > filter/convert > > > > > > > them > > > > > > > > > in RegionObserver.postScannerNext(). > > > > > > > > > Of course ideally we would never generate any Dummy cells > in > > > the > > > > > > first > > > > > > > > > place. > > > > > > > > > > > > > > > > > > > > > > > > > > > > >> > > > > > > > > > > >> > in that case we'd need > > > > > > > > > > >> > to check and convert to a heartbeat scan result > > somehow > > > > > > > > > > >> > > > > > > > > > > >> This needs changes in HBase only, which I don't think > > > HBase > > > > > > would > > > > > > > > > > >> (should) allow. > > > > > > > > > > >> > > > > > > > > > > >> > Is Hbase 2/3 wire compatible enough that connecting > > with > > > > > HBase > > > > > > > 2.x > > > > > > > > > > >> clients > > > > > > > > > > >> > to Hbase 3 even a possibility ? > > > > > > > > > > >> > > > > > > > > > > >> Yes, wire compatibility is important. When this > happens, > > > the > > > > > > only > > > > > > > > > thing > > > > > > > > > > >> we can do is set the page timeout high enough that we > > > never > > > > > have > > > > > > > to > > > > > > > > > send > > > > > > > > > > >> the dummy result to the client, or disable the paging > > > > feature. > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > > >> On Thu, Nov 13, 2025 at 11:22 PM Istvan Toth < > > > > > [email protected]> > > > > > > > > > wrote: > > > > > > > > > > >> > > > > > > > > > > >>> I've been struggling with errors on the region moving > > > tests > > > > > on > > > > > > my > > > > > > > > > HBase > > > > > > > > > > >>> 3.0 > > > > > > > > > > >>> WIP branch and have finally tracked the problems down > > to > > > > > > > Phoenix's > > > > > > > > > > dummy > > > > > > > > > > >>> Cells (as well as some built-in assumptions in > Phoenix > > > > which > > > > > > are > > > > > > > > not > > > > > > > > > > true > > > > > > > > > > >>> for Hbase 3, see PHOENIX-7728 > > > > > > > > > > >>> <https://issues.apache.org/jira/browse/PHOENIX-7728 > >) > > > > > > > > > > >>> > > > > > > > > > > >>> HBase is not aware that these are dummy cells, and is > > > > > > considering > > > > > > > > the > > > > > > > > > > >>> rows > > > > > > > > > > >>> as already processed when retrying scans after the > > region > > > > > goes > > > > > > > away > > > > > > > > > > from > > > > > > > > > > >>> under the scan, i.e. it restarts the scan from AFTER > > the > > > > > dummy > > > > > > > > cell's > > > > > > > > > > >>> rowkey, leading to the scan skipping rows. > > > > > > > > > > >>> > > > > > > > > > > >>> I have been able to fix the tests by hacking Hbase to > > > > ignore > > > > > > > these > > > > > > > > > > dummy > > > > > > > > > > >>> cells (and fixing the phoenix side problems described > > in > > > > > > > > PHOENIX-7728 > > > > > > > > > > >>> <https://issues.apache.org/jira/browse/PHOENIX-7728 > >), > > > > but I > > > > > > > don't > > > > > > > > > > think > > > > > > > > > > >>> that hacking HBase to work with dummy cells is the > way > > to > > > > go > > > > > > (or > > > > > > > > even > > > > > > > > > > if > > > > > > > > > > >>> that would be accepted by HBase). > > > > > > > > > > >>> > > > > > > > > > > >>> AFAIU the dummy cells were added back in the HBase > 1.x > > > when > > > > > > there > > > > > > > > was > > > > > > > > > > no > > > > > > > > > > >>> other way to ensure timely responses from the server. > > > > > > > > > > >>> > > > > > > > > > > >>> HBase 2 has introduced the keepalive/cursor > mechanics, > > > > which > > > > > > IUC > > > > > > > > > serves > > > > > > > > > > >>> the > > > > > > > > > > >>> exact same purpose at the Phoenix dummy cells. > > > > > > > > > > >>> > > > > > > > > > > >>> I propose dropping the dummy cell mechanics from > > Phoenix, > > > > and > > > > > > > using > > > > > > > > > the > > > > > > > > > > >>> HBase keepalive/cursor mechanics instead (we may not > > even > > > > > need > > > > > > > the > > > > > > > > > > >>> cursors). > > > > > > > > > > >>> > > > > > > > > > > >>> If we cannot find a better way to shortcut some > > > processing > > > > in > > > > > > > > Phoenix > > > > > > > > > > we > > > > > > > > > > >>> may need to keep dummy cells internally, but we have > to > > > > make > > > > > > sure > > > > > > > > > that > > > > > > > > > > >>> they > > > > > > > > > > >>> never appear on the wire and reach the client. (i.e. > in > > > > that > > > > > > case > > > > > > > > > we'd > > > > > > > > > > >>> need > > > > > > > > > > >>> to check and convert to a heartbeat scan result > > somehow) > > > > > > > > > > >>> > > > > > > > > > > >>> We will also need to consider backwards > compatibility. > > > > > > > > > > >>> > > > > > > > > > > >>> Is Hbase 2/3 wire compatible enough that connecting > > with > > > > > HBase > > > > > > > 2.x > > > > > > > > > > >>> clients > > > > > > > > > > >>> to Hbase 3 even a possibility ? > > > > > > > > > > >>> > > > > > > > > > > >>> Do we want to support that ? > > > > > > > > > > >>> > > > > > > > > > > >>> When using Hbase 2.x, if Phoenix starts to use the > > HBase > > > > > > > keepalive > > > > > > > > > > >>> mechanics, will old clients work with that without > > > changes, > > > > > or > > > > > > do > > > > > > > > we > > > > > > > > > > need > > > > > > > > > > >>> to keep sending Dummy cells for older clients ? > > > > > > > > > > >>> > > > > > > > > > > >>> Looking forward to hearing your take, > > > > > > > > > > >>> > > > > > > > > > > >>> Istvan > > > > > > > > > > >>> > > > > > > > > > > >> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > *István Tóth* | Sr. Staff Software Engineer > > > > > > > > > *Email*: [email protected] > > > > > > > > > cloudera.com <https://www.cloudera.com> > > > > > > > > > [image: Cloudera] <https://www.cloudera.com/> > > > > > > > > > [image: Cloudera on Twitter] <https://twitter.com/cloudera > > > > > > > [image: > > > > > > > > > Cloudera on Facebook] <https://www.facebook.com/cloudera> > > > > [image: > > > > > > > > Cloudera > > > > > > > > > on LinkedIn] <https://www.linkedin.com/company/cloudera> > > > > > > > > > ------------------------------ > > > > > > > > > ------------------------------ > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > *István Tóth* | Sr. Staff Software Engineer > > > > > > *Email*: [email protected] > > > > > > cloudera.com <https://www.cloudera.com> > > > > > > [image: Cloudera] <https://www.cloudera.com/> > > > > > > [image: Cloudera on Twitter] <https://twitter.com/cloudera> > > [image: > > > > > > Cloudera on Facebook] <https://www.facebook.com/cloudera> > [image: > > > > > Cloudera > > > > > > on LinkedIn] <https://www.linkedin.com/company/cloudera> > > > > > > ------------------------------ > > > > > > ------------------------------ > > > > > > > > > > > > > > > > > > > > > > > -- > > > > *István Tóth* | Sr. Staff Software Engineer > > > > *Email*: [email protected] > > > > cloudera.com <https://www.cloudera.com> > > > > [image: Cloudera] <https://www.cloudera.com/> > > > > [image: Cloudera on Twitter] <https://twitter.com/cloudera> [image: > > > > Cloudera on Facebook] <https://www.facebook.com/cloudera> [image: > > > Cloudera > > > > on LinkedIn] <https://www.linkedin.com/company/cloudera> > > > > ------------------------------ > > > > ------------------------------ > > > > > > > > > > > > > -- > > *István Tóth* | Sr. Staff Software Engineer > > *Email*: [email protected] > > cloudera.com <https://www.cloudera.com> > > [image: Cloudera] <https://www.cloudera.com/> > > [image: Cloudera on Twitter] <https://twitter.com/cloudera> [image: > > Cloudera on Facebook] <https://www.facebook.com/cloudera> [image: > Cloudera > > on LinkedIn] <https://www.linkedin.com/company/cloudera> > > ------------------------------ > > ------------------------------ > > > -- *István Tóth* | Sr. Staff Software Engineer *Email*: [email protected] cloudera.com <https://www.cloudera.com> [image: Cloudera] <https://www.cloudera.com/> [image: Cloudera on Twitter] <https://twitter.com/cloudera> [image: Cloudera on Facebook] <https://www.facebook.com/cloudera> [image: Cloudera on LinkedIn] <https://www.linkedin.com/company/cloudera> ------------------------------ ------------------------------
