Fix SkipScan path generation with constant DISTINCT column #3661

svenklemm · 2021-10-06T17:10:02Z

When a DISTINCT query has a WHERE clause that constifies the
DISTINCT column the query might use an index that does not have
include the DISTINCT column even though it is referenced in the
ORDER BY clause. The skipscan path generation would error on any
path with such a configuration. This patch changes the path
generation code to skip generating SkipScan path under these
circumstances.

Fixes #3629

fabriziomello · 2021-10-06T17:56:47Z

Just need to add tsl/test/expected/plan_skip_scan-12.out, other than that LGTM

codecov · 2021-10-06T18:37:51Z

Codecov Report

Merging #3661 (a365932) into master (74ca546) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3661   +/-   ##
=======================================
  Coverage   90.79%   90.79%           
=======================================
  Files         212      212           
  Lines       36548    36549    +1     
=======================================
+ Hits        33182    33185    +3     
+ Misses       3366     3364    -2

Impacted Files	Coverage Δ
tsl/src/nodes/skip_scan/planner.c	`96.35% <100.00%> (+0.84%)`	⬆️
src/bgw/scheduler.c	`83.04% <0.00%> (-0.88%)`	⬇️
tsl/src/nodes/data_node_dispatch.c	`97.10% <0.00%> (-0.25%)`	⬇️
tsl/src/bgw_policy/job.c	`96.85% <0.00%> (-0.01%)`	⬇️
src/loader/bgw_message_queue.c	`88.15% <0.00%> (+2.63%)`	⬆️

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 74ca546...a365932. Read the comment docs.

gayyappan · 2021-10-07T13:16:45Z

tsl/test/expected/plan_skip_scan-13.out

@@ -3909,3 +3909,35 @@ EXPLAIN (costs off, timing off, summary off) SELECT DISTINCT ON (dev_name) dev_n
                     Index Cond: (dev_name > NULL::text)
 (15 rows)

+-- #3629 skipscan with constant skipscan column in where clause


This comment is a bit misleading. We don't have an index with "a". So cannot apply skipscan?

gayyappan · 2021-10-07T13:29:49Z

tsl/src/nodes/skip_scan/planner.c

@@ -536,7 +536,21 @@ build_skip_qual(PlannerInfo *root, SkipScanPath *skip_scan_path, IndexPath *inde
 	Oid column_type = exprType((Node *) var);
 	Oid column_collation = get_typcollation(column_type);
 	TypeCacheEntry *tce = lookup_type_cache(column_type, 0);
+
+	/*
+	 * If we have an order by clause with columns that have constraints in the WHERE clause


Suggested change

* If we have an order by clause with columns that have constraints in the WHERE clause

Skipscan is not applicable for the following case:

We might have a path with an index that produces the correct pathkeys for the target ordering without actually including all the columns of the ORDER BY. If the path uses an index that does not include the distinct column, we cannot use it for skipscan and have to discard this path from skipscan generation.

This happens, for instance, when we have an order by clause ( like ORDER BY a, b) with constraints in the WHERE clause (like WHERE a = <constant>) . "a" can now be removed from the Pathkeys (since it is a constant) and the query can be satisfied by using an index on just column "b".

gayyappan

Changes look good. Minor comment edits requested.

When a DISTINCT query has a WHERE clause that constifies the DISTINCT column the query might use an index that does not have include the DISTINCT column even though it is referenced in the ORDER BY clause. The skipscan path generation would error on any path with such a configuration. This patch changes the path generation code to skip generating SkipScan path under these circumstances. Fixes timescale#3629

@binakot

This release adds major new features since the 2.4.2 release. We deem it moderate priority for upgrading This release adds several and long-awaited/wanted features: * Continuous Aggregates for Distributed Hypertables * Support for PostgreSQL 14 * Experimental: Support for timezones in `time_bucket_ng()`, including the `origin` argument This release also includes several bug fixes. **Major Features** * timescale#3435 Add continuous aggregates for distributed hypertables * timescale#3034 Add support for PostgreSQL 14 * timescale#3505 Add support for timezones in `time_bucket_ng()` **Minor Features** * timescale#3598 Improve evaluation of stable functions such as now() on access node **Bugfixes** * timescale#3580 Fix memory context bug executing TRUNCATE * timescale#3654 Fix index attnum mapping in reorder_chunk * timescale#3661 Fix SkipScan path generation with constant DISTINCT column * timescale#3708 Fix crash in get_aggsplit * timescale#3709 Fix ordered append pathkey check * timescale#3728 Fix SkipScan with varchar column **Thanks** * @binakot and @sebvett for reporting an issue with DISTINCT queries * @hardikm10, @DavidPavlicek and @pafiti for reporting bugs on TRUNCATE * @mjf for reporting an issue with ordered append and JOINs * @phemmer for reporting the issues on multinode with aggregate queries and evaluation of now() Disable-check: commit-count

@binakot

This release adds major new features since the 2.4.2 release. We deem it moderate priority for upgrading This release adds several and long-awaited/wanted features: * Continuous Aggregates for Distributed Hypertables * Support for PostgreSQL 14 * Experimental: Support for timezones in `time_bucket_ng()`, including the `origin` argument This release also includes several bug fixes. **Major Features** * timescale#3435 Add continuous aggregates for distributed hypertables * timescale#3034 Add support for PostgreSQL 14 * timescale#3505 Add support for timezones in `time_bucket_ng()` **Minor Features** * timescale#3598 Improve evaluation of stable functions such as now() on access node **Bugfixes** * timescale#3580 Fix memory context bug executing TRUNCATE * timescale#3654 Fix index attnum mapping in reorder_chunk * timescale#3661 Fix SkipScan path generation with constant DISTINCT column * timescale#3708 Fix crash in get_aggsplit * timescale#3709 Fix ordered append pathkey check * timescale#3728 Fix SkipScan with varchar column **Thanks** * @binakot and @sebvett for reporting an issue with DISTINCT queries * @hardikm10, @DavidPavlicek and @pafiti for reporting bugs on TRUNCATE * @mjf for reporting an issue with ordered append and JOINs * @phemmer for reporting the issues on multinode with aggregate queries and evaluation of now() Disable-check: commit-count

@binakot

This release adds major new features since the 2.4.2 release. We deem it moderate priority for upgrading This release adds several and long-awaited/wanted features: * Continuous Aggregates for Distributed Hypertables * Support for PostgreSQL 14 * Experimental: Support for timezones in `time_bucket_ng()`, including the `origin` argument This release also includes several bug fixes. **Major Features** * timescale#3435 Add continuous aggregates for distributed hypertables * timescale#3034 Add support for PostgreSQL 14 * timescale#3505 Add support for timezones in `time_bucket_ng()` **Minor Features** * timescale#3598 Improve evaluation of stable functions such as now() on access node **Bugfixes** * timescale#3580 Fix memory context bug executing TRUNCATE * timescale#3654 Fix index attnum mapping in reorder_chunk * timescale#3661 Fix SkipScan path generation with constant DISTINCT column * timescale#3708 Fix crash in get_aggsplit * timescale#3709 Fix ordered append pathkey check * timescale#3728 Fix SkipScan with varchar column **Thanks** * @binakot and @sebvett for reporting an issue with DISTINCT queries * @hardikm10, @DavidPavlicek and @pafiti for reporting bugs on TRUNCATE * @mjf for reporting an issue with ordered append and JOINs * @phemmer for reporting the issues on multinode with aggregate queries and evaluation of now() Disable-check: commit-count

@binakot

This release adds major new features since the 2.4.2 release. We deem it moderate priority for upgrading This release adds several and long-awaited/wanted features: * Continuous Aggregates for Distributed Hypertables * Support for PostgreSQL 14 * Experimental: Support for timezones in `time_bucket_ng()`, including the `origin` argument This release also includes several bug fixes. **Major Features** * timescale#3435 Add continuous aggregates for distributed hypertables * timescale#3034 Add support for PostgreSQL 14 * timescale#3505 Add support for timezones in `time_bucket_ng()` **Minor Features** * timescale#3598 Improve evaluation of stable functions such as now() on access node **Bugfixes** * timescale#3580 Fix memory context bug executing TRUNCATE * timescale#3654 Fix index attnum mapping in reorder_chunk * timescale#3661 Fix SkipScan path generation with constant DISTINCT column * timescale#3708 Fix crash in get_aggsplit * timescale#3709 Fix ordered append pathkey check * timescale#3728 Fix SkipScan with varchar column **Thanks** * @binakot and @sebvett for reporting an issue with DISTINCT queries * @hardikm10, @DavidPavlicek and @pafiti for reporting bugs on TRUNCATE * @mjf for reporting an issue with ordered append and JOINs * @phemmer for reporting the issues on multinode with aggregate queries and evaluation of now() Disable-check: commit-count

@binakot

This release adds major new features since the 2.4.2 release. We deem it moderate priority for upgrading This release adds several and long-awaited/wanted features: * Continuous Aggregates for Distributed Hypertables * Support for PostgreSQL 14 * Experimental: Support for timezones in `time_bucket_ng()`, including the `origin` argument This release also includes several bug fixes. **Major Features** * timescale#3435 Add continuous aggregates for distributed hypertables * timescale#3034 Add support for PostgreSQL 14 * timescale#3505 Add support for timezones in `time_bucket_ng()` **Minor Features** * timescale#3598 Improve evaluation of stable functions such as now() on access node **Bugfixes** * timescale#3580 Fix memory context bug executing TRUNCATE * timescale#3654 Fix index attnum mapping in reorder_chunk * timescale#3661 Fix SkipScan path generation with constant DISTINCT column * timescale#3708 Fix crash in get_aggsplit * timescale#3709 Fix ordered append pathkey check * timescale#3728 Fix SkipScan with varchar column **Thanks** * @binakot and @sebvett for reporting an issue with DISTINCT queries * @hardikm10, @DavidPavlicek and @pafiti for reporting bugs on TRUNCATE * @mjf for reporting an issue with ordered append and JOINs * @phemmer for reporting the issues on multinode with aggregate queries and evaluation of now() Disable-check: commit-count

@binakot

This release adds major new features since the 2.4.2 release. We deem it moderate priority for upgrading. This release includes these noteworthy features: * Continuous Aggregates for Distributed Hypertables * Support for PostgreSQL 14 * Experimental: Support for timezones in `time_bucket_ng()`, including the `origin` argument This release also includes several bug fixes. **Features** * timescale#3034 Add support for PostgreSQL 14 * timescale#3435 Add continuous aggregates for distributed hypertables * timescale#3505 Add support for timezones in `time_bucket_ng()` * timescale#3598 Improve evaluation of stable functions such as now() on access node * timescale#3717 Support transparent decompression on individual chunks **Bugfixes** * timescale#3580 Fix memory context bug executing TRUNCATE * timescale#3592 Allow alter column type on distributed hypertable * timescale#3618 Fix execution of refresh_caggs from user actions * timescale#3625 Add shared dependencies when creating chunk * timescale#3626 Fix memory context bug executing TRUNCATE * timescale#3627 Schema qualify UDTs in multi-node * timescale#3638 Allow owner change of a data node * timescale#3654 Fix index attnum mapping in reorder_chunk * timescale#3661 Fix SkipScan path generation with constant DISTINCT column * timescale#3667 Fix compress_policy for multi txn handling * timescale#3673 Fix distributed hypertable DROP within a procedure * timescale#3701 Allow anyone to use size utilities on distributed hypertables * timescale#3708 Fix crash in get_aggsplit * timescale#3709 Fix ordered append pathkey check * timescale#3712 Fix GRANT/REVOKE ALL IN SCHEMA handling * timescale#3724 Fix inserts into compressed chunks on hypertables with caggs * timescale#3727 Fix DirectFunctionCall crash in distributed_exec * timescale#3728 Fix SkipScan with varchar column * timescale#3733 Fix ANALYZE crash with custom statistics for custom types * timescale#3747 Always reset expr context in DecompressChunk **Thanks** * @binakot and @sebvett for reporting an issue with DISTINCT queries * @hardikm10, @DavidPavlicek and @pafiti for reporting bugs on TRUNCATE * @mjf for reporting an issue with ordered append and JOINs * @phemmer for reporting the issues on multinode with aggregate queries and evaluation of now() * @abolognino for reporting an issue with INSERTs into compressed hypertables that have cagg * @tanglebones for reporting the ANALYZE crash with custom types on multinode

@binakot

This release adds major new features since the 2.4.2 release. We deem it moderate priority for upgrading. This release includes these noteworthy features: * Continuous Aggregates for Distributed Hypertables * Support for PostgreSQL 14 * Experimental: Support for timezones in `time_bucket_ng()`, including the `origin` argument This release also includes several bug fixes. **Features** * timescale#3034 Add support for PostgreSQL 14 * timescale#3435 Add continuous aggregates for distributed hypertables * timescale#3505 Add support for timezones in `time_bucket_ng()` **Bugfixes** * timescale#3580 Fix memory context bug executing TRUNCATE * timescale#3592 Allow alter column type on distributed hypertable * timescale#3598 Improve evaluation of stable functions such as now() on access node * timescale#3618 Fix execution of refresh_caggs from user actions * timescale#3625 Add shared dependencies when creating chunk * timescale#3626 Fix memory context bug executing TRUNCATE * timescale#3627 Schema qualify UDTs in multi-node * timescale#3638 Allow owner change of a data node * timescale#3654 Fix index attnum mapping in reorder_chunk * timescale#3661 Fix SkipScan path generation with constant DISTINCT column * timescale#3667 Fix compress_policy for multi txn handling * timescale#3673 Fix distributed hypertable DROP within a procedure * timescale#3701 Allow anyone to use size utilities on distributed hypertables * timescale#3708 Fix crash in get_aggsplit * timescale#3709 Fix ordered append pathkey check * timescale#3712 Fix GRANT/REVOKE ALL IN SCHEMA handling * timescale#3717 Support transparent decompression on individual chunks * timescale#3724 Fix inserts into compressed chunks on hypertables with caggs * timescale#3727 Fix DirectFunctionCall crash in distributed_exec * timescale#3728 Fix SkipScan with varchar column * timescale#3733 Fix ANALYZE crash with custom statistics for custom types * timescale#3747 Always reset expr context in DecompressChunk **Thanks** * @binakot and @sebvett for reporting an issue with DISTINCT queries * @hardikm10, @DavidPavlicek and @pafiti for reporting bugs on TRUNCATE * @mjf for reporting an issue with ordered append and JOINs * @phemmer for reporting the issues on multinode with aggregate queries and evaluation of now() * @abolognino for reporting an issue with INSERTs into compressed hypertables that have cagg * @tanglebones for reporting the ANALYZE crash with custom types on multinode

@binakot

This release adds major new features since the 2.4.2 release. We deem it moderate priority for upgrading. This release includes these noteworthy features: * Continuous Aggregates for Distributed Hypertables * Support for PostgreSQL 14 * Experimental: Support for timezones in `time_bucket_ng()`, including the `origin` argument This release also includes several bug fixes. **Features** * #3034 Add support for PostgreSQL 14 * #3435 Add continuous aggregates for distributed hypertables * #3505 Add support for timezones in `time_bucket_ng()` **Bugfixes** * #3580 Fix memory context bug executing TRUNCATE * #3592 Allow alter column type on distributed hypertable * #3598 Improve evaluation of stable functions such as now() on access node * #3618 Fix execution of refresh_caggs from user actions * #3625 Add shared dependencies when creating chunk * #3626 Fix memory context bug executing TRUNCATE * #3627 Schema qualify UDTs in multi-node * #3638 Allow owner change of a data node * #3654 Fix index attnum mapping in reorder_chunk * #3661 Fix SkipScan path generation with constant DISTINCT column * #3667 Fix compress_policy for multi txn handling * #3673 Fix distributed hypertable DROP within a procedure * #3701 Allow anyone to use size utilities on distributed hypertables * #3708 Fix crash in get_aggsplit * #3709 Fix ordered append pathkey check * #3712 Fix GRANT/REVOKE ALL IN SCHEMA handling * #3717 Support transparent decompression on individual chunks * #3724 Fix inserts into compressed chunks on hypertables with caggs * #3727 Fix DirectFunctionCall crash in distributed_exec * #3728 Fix SkipScan with varchar column * #3733 Fix ANALYZE crash with custom statistics for custom types * #3747 Always reset expr context in DecompressChunk **Thanks** * @binakot and @sebvett for reporting an issue with DISTINCT queries * @hardikm10, @DavidPavlicek and @pafiti for reporting bugs on TRUNCATE * @mjf for reporting an issue with ordered append and JOINs * @phemmer for reporting the issues on multinode with aggregate queries and evaluation of now() * @abolognino for reporting an issue with INSERTs into compressed hypertables that have cagg * @tanglebones for reporting the ANALYZE crash with custom types on multinode

@binakot

This release adds major new features since the 2.4.2 release. We deem it moderate priority for upgrading. This release includes these noteworthy features: * Continuous Aggregates for Distributed Hypertables * Support for PostgreSQL 14 * Experimental: Support for timezones in `time_bucket_ng()`, including the `origin` argument This release also includes several bug fixes. **Features** * #3034 Add support for PostgreSQL 14 * #3435 Add continuous aggregates for distributed hypertables * #3505 Add support for timezones in `time_bucket_ng()` **Bugfixes** * #3580 Fix memory context bug executing TRUNCATE * #3592 Allow alter column type on distributed hypertable * #3598 Improve evaluation of stable functions such as now() on access node * #3618 Fix execution of refresh_caggs from user actions * #3625 Add shared dependencies when creating chunk * #3626 Fix memory context bug executing TRUNCATE * #3627 Schema qualify UDTs in multi-node * #3638 Allow owner change of a data node * #3654 Fix index attnum mapping in reorder_chunk * #3661 Fix SkipScan path generation with constant DISTINCT column * #3667 Fix compress_policy for multi txn handling * #3673 Fix distributed hypertable DROP within a procedure * #3701 Allow anyone to use size utilities on distributed hypertables * #3708 Fix crash in get_aggsplit * #3709 Fix ordered append pathkey check * #3712 Fix GRANT/REVOKE ALL IN SCHEMA handling * #3717 Support transparent decompression on individual chunks * #3724 Fix inserts into compressed chunks on hypertables with caggs * #3727 Fix DirectFunctionCall crash in distributed_exec * #3728 Fix SkipScan with varchar column * #3733 Fix ANALYZE crash with custom statistics for custom types * #3747 Always reset expr context in DecompressChunk **Thanks** * @binakot and @sebvett for reporting an issue with DISTINCT queries * @hardikm10, @DavidPavlicek and @pafiti for reporting bugs on TRUNCATE * @mjf for reporting an issue with ordered append and JOINs * @phemmer for reporting the issues on multinode with aggregate queries and evaluation of now() * @abolognino for reporting an issue with INSERTs into compressed hypertables that have cagg * @tanglebones for reporting the ANALYZE crash with custom types on multinode

@binakot

This release adds major new features since the 2.4.2 release. We deem it moderate priority for upgrading. This release includes these noteworthy features: * Continuous Aggregates for Distributed Hypertables * Support for PostgreSQL 14 * Experimental: Support for timezones in `time_bucket_ng()`, including the `origin` argument This release also includes several bug fixes. **Features** * #3034 Add support for PostgreSQL 14 * #3435 Add continuous aggregates for distributed hypertables * #3505 Add support for timezones in `time_bucket_ng()` **Bugfixes** * #3580 Fix memory context bug executing TRUNCATE * #3592 Allow alter column type on distributed hypertable * #3598 Improve evaluation of stable functions such as now() on access node * #3618 Fix execution of refresh_caggs from user actions * #3625 Add shared dependencies when creating chunk * #3626 Fix memory context bug executing TRUNCATE * #3627 Schema qualify UDTs in multi-node * #3638 Allow owner change of a data node * #3654 Fix index attnum mapping in reorder_chunk * #3661 Fix SkipScan path generation with constant DISTINCT column * #3667 Fix compress_policy for multi txn handling * #3673 Fix distributed hypertable DROP within a procedure * #3701 Allow anyone to use size utilities on distributed hypertables * #3708 Fix crash in get_aggsplit * #3709 Fix ordered append pathkey check * #3712 Fix GRANT/REVOKE ALL IN SCHEMA handling * #3717 Support transparent decompression on individual chunks * #3724 Fix inserts into compressed chunks on hypertables with caggs * #3727 Fix DirectFunctionCall crash in distributed_exec * #3728 Fix SkipScan with varchar column * #3733 Fix ANALYZE crash with custom statistics for custom types * #3747 Always reset expr context in DecompressChunk **Thanks** * @binakot and @sebvett for reporting an issue with DISTINCT queries * @hardikm10, @DavidPavlicek and @pafiti for reporting bugs on TRUNCATE * @mjf for reporting an issue with ordered append and JOINs * @phemmer for reporting the issues on multinode with aggregate queries and evaluation of now() * @abolognino for reporting an issue with INSERTs into compressed hypertables that have cagg * @tanglebones for reporting the ANALYZE crash with custom types on multinode

@binakot

This release adds major new features since the 2.4.2 release. We deem it moderate priority for upgrading. This release includes these noteworthy features: * Continuous Aggregates for Distributed Hypertables * Support for PostgreSQL 14 * Experimental: Support for timezones in `time_bucket_ng()`, including the `origin` argument This release also includes several bug fixes. **Features** * #3034 Add support for PostgreSQL 14 * #3435 Add continuous aggregates for distributed hypertables * #3505 Add support for timezones in `time_bucket_ng()` **Bugfixes** * #3580 Fix memory context bug executing TRUNCATE * #3592 Allow alter column type on distributed hypertable * #3598 Improve evaluation of stable functions such as now() on access node * #3618 Fix execution of refresh_caggs from user actions * #3625 Add shared dependencies when creating chunk * #3626 Fix memory context bug executing TRUNCATE * #3627 Schema qualify UDTs in multi-node * #3638 Allow owner change of a data node * #3654 Fix index attnum mapping in reorder_chunk * #3661 Fix SkipScan path generation with constant DISTINCT column * #3667 Fix compress_policy for multi txn handling * #3673 Fix distributed hypertable DROP within a procedure * #3701 Allow anyone to use size utilities on distributed hypertables * #3708 Fix crash in get_aggsplit * #3709 Fix ordered append pathkey check * #3712 Fix GRANT/REVOKE ALL IN SCHEMA handling * #3717 Support transparent decompression on individual chunks * #3724 Fix inserts into compressed chunks on hypertables with caggs * #3727 Fix DirectFunctionCall crash in distributed_exec * #3728 Fix SkipScan with varchar column * #3733 Fix ANALYZE crash with custom statistics for custom types * #3747 Always reset expr context in DecompressChunk **Thanks** * @binakot and @sebvett for reporting an issue with DISTINCT queries * @hardikm10, @DavidPavlicek and @pafiti for reporting bugs on TRUNCATE * @mjf for reporting an issue with ordered append and JOINs * @phemmer for reporting the issues on multinode with aggregate queries and evaluation of now() * @abolognino for reporting an issue with INSERTs into compressed hypertables that have cagg * @tanglebones for reporting the ANALYZE crash with custom types on multinode

svenklemm requested a review from a team as a code owner October 6, 2021 17:10

svenklemm requested review from afiskon, akuzm, duncan-tsdb, gayyappan, mkindahl, fabriziomello, mfundul, nikkhils and pmwkaa and removed request for a team October 6, 2021 17:10

svenklemm force-pushed the i3629 branch 3 times, most recently from a30cc03 to d4a99d9 Compare October 6, 2021 17:22

svenklemm self-assigned this Oct 6, 2021

svenklemm added this to the TimescaleDB 2.5 milestone Oct 6, 2021

svenklemm added the bug label Oct 6, 2021

svenklemm force-pushed the i3629 branch from d4a99d9 to 94720c4 Compare October 6, 2021 18:22

fabriziomello approved these changes Oct 6, 2021

View reviewed changes

svenklemm force-pushed the i3629 branch 3 times, most recently from 075da3c to 43aebc3 Compare October 7, 2021 09:02

gayyappan reviewed Oct 7, 2021

View reviewed changes

gayyappan approved these changes Oct 7, 2021

View reviewed changes

svenklemm force-pushed the i3629 branch from 43aebc3 to 5a46093 Compare October 7, 2021 14:23

svenklemm force-pushed the i3629 branch from 5a46093 to a365932 Compare October 7, 2021 14:40

svenklemm merged commit 9e53cbb into timescale:master Oct 7, 2021

fabriziomello mentioned this pull request Oct 26, 2021

Release 2.5.0 #3744

Merged

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Fix SkipScan path generation with constant DISTINCT column #3661

Fix SkipScan path generation with constant DISTINCT column #3661

svenklemm commented Oct 6, 2021

fabriziomello commented Oct 6, 2021

codecov bot commented Oct 6, 2021 •

edited

Loading

gayyappan Oct 7, 2021

gayyappan Oct 7, 2021

gayyappan left a comment

-	 * If we have an order by clause with columns that have constraints in the WHERE clause
+Skipscan is not applicable for the following case:
+We might have a path with an index that produces the correct pathkeys for the target ordering without actually including all the columns of the ORDER BY. If the path uses an index that does not include the distinct column, we cannot use it for skipscan and have to discard this path from skipscan generation.
+ This happens, for instance, when we have an order by clause ( like ORDER BY a, b) with constraints in the WHERE clause (like WHERE a = <constant>) . "a" can now be removed from the Pathkeys  (since it is a constant) and the query can be satisfied by using an index on just column "b".

Fix SkipScan path generation with constant DISTINCT column #3661

Fix SkipScan path generation with constant DISTINCT column #3661

Conversation

svenklemm commented Oct 6, 2021

fabriziomello commented Oct 6, 2021

codecov bot commented Oct 6, 2021 • edited Loading

Codecov Report

gayyappan Oct 7, 2021

Choose a reason for hiding this comment

gayyappan Oct 7, 2021

Choose a reason for hiding this comment

gayyappan left a comment

Choose a reason for hiding this comment

codecov bot commented Oct 6, 2021 •

edited

Loading