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sql: add support for cursors #30352

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ghost opened this issue Sep 18, 2018 · 11 comments
Closed

sql: add support for cursors #30352

ghost opened this issue Sep 18, 2018 · 11 comments
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C-question A question rather than an issue. No code/spec/doc change needed. O-community Originated from the community

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@ghost
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ghost commented Sep 18, 2018

When using other databases, such as Oracle/PG, I can process data row by row through a cursor, but CockroachDB does not support it. Can you tell me which version is supported?
@knz knz added O-community Originated from the community C-question A question rather than an issue. No code/spec/doc change needed. labels Sep 18, 2018
@awoods187
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Hi ethanhexd, we don't support cursors yet. I understand that you are asking about cursors in relation to pagination. In our engineer's experience, cursors are generally not a great architecture solution as they force the server to keep state. Server pagination does not scale well and cursors are rarely recommended even if the feature itself is implemented.

We actually recommended doing “client-side pagination” by retrieving a set of records with a limit, and then checking the index key of the last row, using that as an index constraint, and then running the query again.

This solution isn't specific to Cockroach but is actually a best practice recommendation for all databases. The reason is that offset has to get the same data as before, just skips the first N. To address this, you have to participate as a client by remembering the index key of the last result set you saw.

Let me know if you have further questions and I hope this helps!

@awoods187 awoods187 mentioned this issue Sep 18, 2018
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@ghost
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ghost commented Sep 19, 2018

Thank you for your reply!
"We actually recommended doing “client-side pagination” by retrieving a set of records with a limit, and then checking the index key of the last row, using that as an index constraint, and then running the query again." means the table must has primary key or index,there will be new problem:
Is it possible to retrieve a set of records with a limit without a primary key or index?

Unfortunately, some tables in our "Data Module" do not have primary key or index.

@knz
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knz commented Oct 23, 2018

All tables without an explicit primary key in CockroachDB automatically get an implicit (hidden) primary key named rowid.

You can use rowid to control the pagination, for example SELECT *, rowid FROM ... WHERE rowid > last_rowid_value

Would this help?

@ghost
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ghost commented Nov 16, 2018

If CockroachDB don't support cursors, we will have a lot of resistance for application developers to use CockroachDB.
Application cannot gradually move to CockroachDB...

@knz
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knz commented Jan 8, 2019

The following page is a good starting point to explain the situation around pagination:
https://www.citusdata.com/blog/2016/03/30/five-ways-to-paginate/

@BramGruneir BramGruneir mentioned this issue Mar 18, 2019
Closed
jordanlewis added a commit to jordanlewis/cockroach that referenced this issue Oct 2, 2019
@jordanlewis
roachtest: add test that aggregates orm blacklist failures
cebc811 
The spreadsheet we discussed is unwieldy - hard to edit and impossible to keep
up to date. If we write down blacklists in code, then we can use an approach
like this to always have an up to date aggregation.

So far it seems like there's just a lot of unknowns to categorize still.

The output today:

```
=== RUN   TestBlacklists
 648: unknown                                                (unknown)
 493: cockroachdb#5807   (sql: Add support for TEMP tables)
 151: cockroachdb#17511  (sql: support stored procedures)
  86: cockroachdb#26097  (sql: make TIMETZ more pg-compatible)
  56: cockroachdb#10735  (sql: support SQL savepoints)
  55: cockroachdb#32552  (multi-dim arrays)
  55: cockroachdb#26508  (sql: restricted DDL / DML inside transactions)
  52: cockroachdb#32565  (sql: support optional TIME precision)
  39: cockroachdb#243    (roadmap: Blob storage)
  33: cockroachdb#26725  (sql: support postgres' API to handle blob storage (incl lo_creat, lo_from_bytea))
  31: cockroachdb#27793  (sql: support custom/user-defined base scalar (primitive) types)
  24: cockroachdb#12123  (sql: Can't drop and replace a table within a transaction)
  24: cockroachdb#26443  (sql: support user-defined schemas between database and table)
  20: cockroachdb#21286  (sql: Add support for geometric types)
  18: cockroachdb#6583   (sql: explicit lock syntax (SELECT FOR {SHARE,UPDATE} {skip locked,nowait}))
  17: cockroachdb#22329  (Support XA distributed transactions in CockroachDB)
  16: cockroachdb#24062  (sql: 32 bit SERIAL type)
  16: cockroachdb#30352  (roadmap:when CockroachDB  will support cursor?)
  12: cockroachdb#27791  (sql: support RANGE types)
   8: cockroachdb#40195  (pgwire: multiple active result sets (portals) not supported)
   8: cockroachdb#6130   (sql: add support for key watches with notifications of changes)
   5: Expected Failure                                       (unknown)
   5: cockroachdb#23468  (sql: support sql arrays of JSONB)
   5: cockroachdb#40854  (sql: set application_name from connection string)
   4: cockroachdb#35879  (sql: `default_transaction_read_only` should also accept 'on' and 'off')
   4: cockroachdb#32610  (sql: can't insert self reference)
   4: cockroachdb#40205  (sql: add non-trivial implementations of FOR UPDATE, FOR NO KEY UPDATE, FOR SHARE, FOR NO KEY SHARE)
   4: cockroachdb#35897  (sql: unknown function: pg_terminate_backend())
   4: cockroachdb#4035   (sql/pgwire: missing support for row count limits in pgwire)
   3: cockroachdb#27796  (sql: support user-defined DOMAIN types)
   3: cockroachdb#3781   (sql: Add Data Type Formatting Functions)
   3: cockroachdb#40476  (sql: support `FOR {UPDATE,SHARE} {SKIP LOCKED,NOWAIT}`)
   3: cockroachdb#35882  (sql: support other character sets)
   2: cockroachdb#10028  (sql: Support view queries with star expansions)
   2: cockroachdb#35807  (sql: INTERVAL output doesn't match PG)
   2: cockroachdb#35902  (sql: large object support)
   2: cockroachdb#40474  (sql: support `SELECT ... FOR UPDATE OF` syntax)
   1: cockroachdb#18846  (sql: Support CIDR column type)
   1: cockroachdb#9682   (sql: implement computed indexes)
   1: cockroachdb#31632  (sql: FK options (deferrable, etc))
   1: cockroachdb#24897  (sql: CREATE OR REPLACE VIEW)
   1: pass?                                                  (unknown)
   1: cockroachdb#36215  (sql: enable setting standard_conforming_strings to off)
   1: cockroachdb#32562  (sql: support SET LOCAL and txn-scoped session variable changes)
   1: cockroachdb#36116  (sql: psychopg: investigate how `'infinity'::timestamp` is presented)
   1: cockroachdb#26732  (sql: support the binary operator: <int> / <float>)
   1: cockroachdb#23299  (sql: support coercing string literals to arrays)
   1: cockroachdb#36115  (sql: psychopg: investigate if datetimetz is being returned instead of datetime)
   1: cockroachdb#26925  (sql: make the CockroachDB integer types more compatible with postgres)
   1: cockroachdb#21085  (sql: WITH RECURSIVE (recursive common table expressions))
   1: cockroachdb#36179  (sql: implicity convert date to timestamp)
   1: cockroachdb#36118  (sql: Cannot parse '24:00' as type time)
   1: cockroachdb#31708  (sql: support current_time)
```

Release justification: non-production change
Release note: None
jordanlewis added a commit to jordanlewis/cockroach that referenced this issue Oct 24, 2019
@jordanlewis
roachtest: add test that aggregates orm blacklist failures
4010eac 
The spreadsheet we discussed is unwieldy - hard to edit and impossible to keep
up to date. If we write down blacklists in code, then we can use an approach
like this to always have an up to date aggregation.

So far it seems like there's just a lot of unknowns to categorize still.

The output today:

```
=== RUN   TestBlacklists
 648: unknown                                                (unknown)
 493: cockroachdb#5807   (sql: Add support for TEMP tables)
 151: cockroachdb#17511  (sql: support stored procedures)
  86: cockroachdb#26097  (sql: make TIMETZ more pg-compatible)
  56: cockroachdb#10735  (sql: support SQL savepoints)
  55: cockroachdb#32552  (multi-dim arrays)
  55: cockroachdb#26508  (sql: restricted DDL / DML inside transactions)
  52: cockroachdb#32565  (sql: support optional TIME precision)
  39: cockroachdb#243    (roadmap: Blob storage)
  33: cockroachdb#26725  (sql: support postgres' API to handle blob storage (incl lo_creat, lo_from_bytea))
  31: cockroachdb#27793  (sql: support custom/user-defined base scalar (primitive) types)
  24: cockroachdb#12123  (sql: Can't drop and replace a table within a transaction)
  24: cockroachdb#26443  (sql: support user-defined schemas between database and table)
  20: cockroachdb#21286  (sql: Add support for geometric types)
  18: cockroachdb#6583   (sql: explicit lock syntax (SELECT FOR {SHARE,UPDATE} {skip locked,nowait}))
  17: cockroachdb#22329  (Support XA distributed transactions in CockroachDB)
  16: cockroachdb#24062  (sql: 32 bit SERIAL type)
  16: cockroachdb#30352  (roadmap:when CockroachDB  will support cursor?)
  12: cockroachdb#27791  (sql: support RANGE types)
   8: cockroachdb#40195  (pgwire: multiple active result sets (portals) not supported)
   8: cockroachdb#6130   (sql: add support for key watches with notifications of changes)
   5: Expected Failure                                       (unknown)
   5: cockroachdb#23468  (sql: support sql arrays of JSONB)
   5: cockroachdb#40854  (sql: set application_name from connection string)
   4: cockroachdb#35879  (sql: `default_transaction_read_only` should also accept 'on' and 'off')
   4: cockroachdb#32610  (sql: can't insert self reference)
   4: cockroachdb#40205  (sql: add non-trivial implementations of FOR UPDATE, FOR NO KEY UPDATE, FOR SHARE, FOR NO KEY SHARE)
   4: cockroachdb#35897  (sql: unknown function: pg_terminate_backend())
   4: cockroachdb#4035   (sql/pgwire: missing support for row count limits in pgwire)
   3: cockroachdb#27796  (sql: support user-defined DOMAIN types)
   3: cockroachdb#3781   (sql: Add Data Type Formatting Functions)
   3: cockroachdb#40476  (sql: support `FOR {UPDATE,SHARE} {SKIP LOCKED,NOWAIT}`)
   3: cockroachdb#35882  (sql: support other character sets)
   2: cockroachdb#10028  (sql: Support view queries with star expansions)
   2: cockroachdb#35807  (sql: INTERVAL output doesn't match PG)
   2: cockroachdb#35902  (sql: large object support)
   2: cockroachdb#40474  (sql: support `SELECT ... FOR UPDATE OF` syntax)
   1: cockroachdb#18846  (sql: Support CIDR column type)
   1: cockroachdb#9682   (sql: implement computed indexes)
   1: cockroachdb#31632  (sql: FK options (deferrable, etc))
   1: cockroachdb#24897  (sql: CREATE OR REPLACE VIEW)
   1: pass?                                                  (unknown)
   1: cockroachdb#36215  (sql: enable setting standard_conforming_strings to off)
   1: cockroachdb#32562  (sql: support SET LOCAL and txn-scoped session variable changes)
   1: cockroachdb#36116  (sql: psychopg: investigate how `'infinity'::timestamp` is presented)
   1: cockroachdb#26732  (sql: support the binary operator: <int> / <float>)
   1: cockroachdb#23299  (sql: support coercing string literals to arrays)
   1: cockroachdb#36115  (sql: psychopg: investigate if datetimetz is being returned instead of datetime)
   1: cockroachdb#26925  (sql: make the CockroachDB integer types more compatible with postgres)
   1: cockroachdb#21085  (sql: WITH RECURSIVE (recursive common table expressions))
   1: cockroachdb#36179  (sql: implicity convert date to timestamp)
   1: cockroachdb#36118  (sql: Cannot parse '24:00' as type time)
   1: cockroachdb#31708  (sql: support current_time)
```

Release justification: non-production change
Release note: None
@JessicaGreben JessicaGreben mentioned this issue Nov 5, 2019
Closed
10 tasks
craig bot pushed a commit that referenced this issue Nov 7, 2019
@jordanlewis
Merge #41252
27fd417 
41252: roachtest: add test that aggregates orm blacklist failures r=jordanlewis a=jordanlewis

The spreadsheet we discussed is unwieldy - hard to edit and impossible to keep
up to date. If we write down blacklists in code, then we can use an approach
like this to always have an up to date aggregation.

So far it seems like there's just a lot of unknowns to categorize still.

The output today:

```
=== RUN   TestBlacklists
 648: unknown                                                (unknown)
 493: #5807   (sql: Add support for TEMP tables)
 151: #17511  (sql: support stored procedures)
  86: #26097  (sql: make TIMETZ more pg-compatible)
  56: #10735  (sql: support SQL savepoints)
  55: #32552  (multi-dim arrays)
  55: #26508  (sql: restricted DDL / DML inside transactions)
  52: #32565  (sql: support optional TIME precision)
  39: #243    (roadmap: Blob storage)
  33: #26725  (sql: support postgres' API to handle blob storage (incl lo_creat, lo_from_bytea))
  31: #27793  (sql: support custom/user-defined base scalar (primitive) types)
  24: #12123  (sql: Can't drop and replace a table within a transaction)
  24: #26443  (sql: support user-defined schemas between database and table)
  20: #21286  (sql: Add support for geometric types)
  18: #6583   (sql: explicit lock syntax (SELECT FOR {SHARE,UPDATE} {skip locked,nowait}))
  17: #22329  (Support XA distributed transactions in CockroachDB)
  16: #24062  (sql: 32 bit SERIAL type)
  16: #30352  (roadmap:when CockroachDB  will support cursor?)
  12: #27791  (sql: support RANGE types)
   8: #40195  (pgwire: multiple active result sets (portals) not supported)
   8: #6130   (sql: add support for key watches with notifications of changes)
   5: Expected Failure                                       (unknown)
   5: #23468  (sql: support sql arrays of JSONB)
   5: #40854  (sql: set application_name from connection string)
   4: #35879  (sql: `default_transaction_read_only` should also accept 'on' and 'off')
   4: #32610  (sql: can't insert self reference)
   4: #40205  (sql: add non-trivial implementations of FOR UPDATE, FOR NO KEY UPDATE, FOR SHARE, FOR NO KEY SHARE)
   4: #35897  (sql: unknown function: pg_terminate_backend())
   4: #4035   (sql/pgwire: missing support for row count limits in pgwire)
   3: #27796  (sql: support user-defined DOMAIN types)
   3: #3781   (sql: Add Data Type Formatting Functions)
   3: #40476  (sql: support `FOR {UPDATE,SHARE} {SKIP LOCKED,NOWAIT}`)
   3: #35882  (sql: support other character sets)
   2: #10028  (sql: Support view queries with star expansions)
   2: #35807  (sql: INTERVAL output doesn't match PG)
   2: #35902  (sql: large object support)
   2: #40474  (sql: support `SELECT ... FOR UPDATE OF` syntax)
   1: #18846  (sql: Support CIDR column type)
   1: #9682   (sql: implement computed indexes)
   1: #31632  (sql: FK options (deferrable, etc))
   1: #24897  (sql: CREATE OR REPLACE VIEW)
   1: pass?                                                  (unknown)
   1: #36215  (sql: enable setting standard_conforming_strings to off)
   1: #32562  (sql: support SET LOCAL and txn-scoped session variable changes)
   1: #36116  (sql: psychopg: investigate how `'infinity'::timestamp` is presented)
   1: #26732  (sql: support the binary operator: <int> / <float>)
   1: #23299  (sql: support coercing string literals to arrays)
   1: #36115  (sql: psychopg: investigate if datetimetz is being returned instead of datetime)
   1: #26925  (sql: make the CockroachDB integer types more compatible with postgres)
   1: #21085  (sql: WITH RECURSIVE (recursive common table expressions))
   1: #36179  (sql: implicity convert date to timestamp)
   1: #36118  (sql: Cannot parse '24:00' as type time)
   1: #31708  (sql: support current_time)
```

Release justification: non-production change
Release note: None

Co-authored-by: Jordan Lewis <jordanthelewis@gmail.com>
@awoods187 awoods187 changed the title roadmap:when CockroachDB will support cursor? sql: add support for cursors Mar 25, 2020
@awoods187 awoods187 removed their assignment Mar 25, 2020
@RoachietheSupportRoach
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Zendesk ticket #4710 has been linked to this issue.

@jordanlewis
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We have pgwire cursors now, does that help? We still don't have SQL-level DECLARE. We also have some duplicate issues around this. I'll close in favor of #41412.

@knz
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knz commented Sep 2, 2020

you'll need to update references to this issue in at least pkg/cmd/roachtest/psycopg_blocklist.go and perhaps other places

@jordanlewis
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D'oh, it wasn't marked as anchored telemetry... I'll re-open this and hide these latest comments :P

@jordanlewis jordanlewis reopened this Sep 2, 2020
@jordanlewis jordanlewis added the X-anchored-telemetry The issue number is anchored by telemetry references. label Sep 2, 2020
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@knz knz closed this as completed Sep 2, 2020
@glennfawcett glennfawcett mentioned this issue Oct 9, 2021
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