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sql: set default for large_full_scan_rows to 0
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In #69371 we set the default for `large_full_scan_rows` to 1000. This
default can be surprising for users of `disallow_full_table_scans`. Now
that #122708 is fixed, let's set the default to 0 so that the exemption
for small tables is opt-in rather than opt-out.

Fixes: #130726

Release note (sql change): Set the default for session variable
`large_full_scan_rows` to 0. This means that by default,
`disallow_full_table_scans` will disallow _all_ full table scans, even
full scans on very small tables. If `large_full_scan_rows` is set > 0,
`disallow_full_table_scans` will allow full scans estimated to read
fewer than `large_full_scan_rows`.
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@michae2
michae2 committed Sep 20, 2024
1 parent 04783da commit 10b9ca1
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Showing 7 changed files with 17 additions and 14 deletions.
4 changes: 2 additions & 2 deletions docs/generated/settings/settings-for-tenants.txt
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Expand Up @@ -190,7 +190,7 @@ This session variable default should now be configured using ALTER ROLE... SET:
sql.defaults.default_int_size integer 8 "the size, in bytes, of an INT type
This cluster setting is being kept to preserve backwards-compatibility.
This session variable default should now be configured using ALTER ROLE... SET: https://www.cockroachlabs.com/docs/stable/alter-role.html" application
sql.defaults.disallow_full_table_scans.enabled boolean false "setting to true rejects queries that have planned a full table scan
sql.defaults.disallow_full_table_scans.enabled boolean false "setting to true rejects queries that have planned a full table scan; set large_full_scan_rows > 0 to allow small full table scans estimated to read fewer than large_full_scan_rows
This cluster setting is being kept to preserve backwards-compatibility.
This session variable default should now be configured using ALTER ROLE... SET: https://www.cockroachlabs.com/docs/stable/alter-role.html" application
sql.defaults.distsql enumeration auto "default distributed SQL execution mode [off = 0, auto = 1, on = 2, always = 3]
Expand Down Expand Up @@ -229,7 +229,7 @@ This session variable default should now be configured using ALTER ROLE... SET:
sql.defaults.intervalstyle enumeration postgres "default value for IntervalStyle session setting [postgres = 0, iso_8601 = 1, sql_standard = 2]
This cluster setting is being kept to preserve backwards-compatibility.
This session variable default should now be configured using ALTER ROLE... SET: https://www.cockroachlabs.com/docs/stable/alter-role.html" application
sql.defaults.large_full_scan_rows float 1000 "default value for large_full_scan_rows session setting which determines the maximum table size allowed for a full scan when disallow_full_table_scans is set to true
sql.defaults.large_full_scan_rows float 0 "default value for large_full_scan_rows session variable which determines the table size at which full scans are considered large and disallowed when disallow_full_table_scans is set to true; set to 0 to reject all full table or full index scans when disallow_full_table_scans is true
This cluster setting is being kept to preserve backwards-compatibility.
This session variable default should now be configured using ALTER ROLE... SET: https://www.cockroachlabs.com/docs/stable/alter-role.html" application
sql.defaults.locality_optimized_partitioned_index_scan.enabled boolean true "default value for locality_optimized_partitioned_index_scan session setting; enables searching for rows in the current region before searching remote regions
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4 changes: 2 additions & 2 deletions docs/generated/settings/settings.html
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Expand Up @@ -217,7 +217,7 @@
<tr><td><div id="setting-sql-defaults-datestyle" class="anchored"><code>sql.defaults.datestyle</code></div></td><td>enumeration</td><td><code>iso, mdy</code></td><td>default value for DateStyle session setting [iso, mdy = 0, iso, dmy = 1, iso, ymd = 2]<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
<tr><td><div id="setting-sql-defaults-default-hash-sharded-index-bucket-count" class="anchored"><code>sql.defaults.default_hash_sharded_index_bucket_count</code></div></td><td>integer</td><td><code>16</code></td><td>used as bucket count if bucket count is not specified in hash sharded index definition<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
<tr><td><div id="setting-sql-defaults-default-int-size" class="anchored"><code>sql.defaults.default_int_size</code></div></td><td>integer</td><td><code>8</code></td><td>the size, in bytes, of an INT type<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
<tr><td><div id="setting-sql-defaults-disallow-full-table-scans-enabled" class="anchored"><code>sql.defaults.disallow_full_table_scans.enabled</code></div></td><td>boolean</td><td><code>false</code></td><td>setting to true rejects queries that have planned a full table scan<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
<tr><td><div id="setting-sql-defaults-disallow-full-table-scans-enabled" class="anchored"><code>sql.defaults.disallow_full_table_scans.enabled</code></div></td><td>boolean</td><td><code>false</code></td><td>setting to true rejects queries that have planned a full table scan; set large_full_scan_rows &gt; 0 to allow small full table scans estimated to read fewer than large_full_scan_rows<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
<tr><td><div id="setting-sql-defaults-distsql" class="anchored"><code>sql.defaults.distsql</code></div></td><td>enumeration</td><td><code>auto</code></td><td>default distributed SQL execution mode [off = 0, auto = 1, on = 2, always = 3]<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
<tr><td><div id="setting-sql-defaults-experimental-alter-column-type-enabled" class="anchored"><code>sql.defaults.experimental_alter_column_type.enabled</code></div></td><td>boolean</td><td><code>false</code></td><td>default value for experimental_alter_column_type session setting; enables the use of ALTER COLUMN TYPE for general conversions<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
<tr><td><div id="setting-sql-defaults-experimental-distsql-planning" class="anchored"><code>sql.defaults.experimental_distsql_planning</code></div></td><td>enumeration</td><td><code>off</code></td><td>default experimental_distsql_planning mode; enables experimental opt-driven DistSQL planning [off = 0, on = 1]<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
Expand All @@ -230,7 +230,7 @@
<tr><td><div id="setting-sql-defaults-implicit-select-for-update-enabled" class="anchored"><code>sql.defaults.implicit_select_for_update.enabled</code></div></td><td>boolean</td><td><code>true</code></td><td>default value for enable_implicit_select_for_update session setting; enables FOR UPDATE locking during the row-fetch phase of mutation statements<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
<tr><td><div id="setting-sql-defaults-insert-fast-path-enabled" class="anchored"><code>sql.defaults.insert_fast_path.enabled</code></div></td><td>boolean</td><td><code>true</code></td><td>default value for enable_insert_fast_path session setting; enables a specialized insert path<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
<tr><td><div id="setting-sql-defaults-intervalstyle" class="anchored"><code>sql.defaults.intervalstyle</code></div></td><td>enumeration</td><td><code>postgres</code></td><td>default value for IntervalStyle session setting [postgres = 0, iso_8601 = 1, sql_standard = 2]<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
<tr><td><div id="setting-sql-defaults-large-full-scan-rows" class="anchored"><code>sql.defaults.large_full_scan_rows</code></div></td><td>float</td><td><code>1000</code></td><td>default value for large_full_scan_rows session setting which determines the maximum table size allowed for a full scan when disallow_full_table_scans is set to true<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
<tr><td><div id="setting-sql-defaults-large-full-scan-rows" class="anchored"><code>sql.defaults.large_full_scan_rows</code></div></td><td>float</td><td><code>0</code></td><td>default value for large_full_scan_rows session variable which determines the table size at which full scans are considered large and disallowed when disallow_full_table_scans is set to true; set to 0 to reject all full table or full index scans when disallow_full_table_scans is true<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
<tr><td><div id="setting-sql-defaults-locality-optimized-partitioned-index-scan-enabled" class="anchored"><code>sql.defaults.locality_optimized_partitioned_index_scan.enabled</code></div></td><td>boolean</td><td><code>true</code></td><td>default value for locality_optimized_partitioned_index_scan session setting; enables searching for rows in the current region before searching remote regions<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
<tr><td><div id="setting-sql-defaults-lock-timeout" class="anchored"><code>sql.defaults.lock_timeout</code></div></td><td>duration</td><td><code>0s</code></td><td>default value for the lock_timeout; default value for the lock_timeout session setting; controls the duration a query is permitted to wait while attempting to acquire a lock on a key or while blocking on an existing lock in order to perform a non-locking read on a key; if set to 0, there is no timeout<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
<tr><td><div id="setting-sql-defaults-on-update-rehome-row-enabled" class="anchored"><code>sql.defaults.on_update_rehome_row.enabled</code></div></td><td>boolean</td><td><code>true</code></td><td>default value for on_update_rehome_row; enables ON UPDATE rehome_row() expressions to trigger on updates<br/>This cluster setting is being kept to preserve backwards-compatibility.<br/>This session variable default should now be configured using <a href="alter-role.html"><code>ALTER ROLE... SET</code></a></td><td>Serverless/Dedicated/Self-Hosted</td></tr>
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13 changes: 8 additions & 5 deletions pkg/sql/exec_util.go
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Original file line number Diff line number Diff line change
Expand Up @@ -633,7 +633,9 @@ var SerialNormalizationMode = settings.RegisterEnumSetting(
var disallowFullTableScans = settings.RegisterBoolSetting(
settings.ApplicationLevel,
`sql.defaults.disallow_full_table_scans.enabled`,
"setting to true rejects queries that have planned a full table scan",
"setting to true rejects queries that have planned a full table scan; set "+
"large_full_scan_rows > 0 to allow small full table scans estimated to "+
"read fewer than large_full_scan_rows",
false,
settings.WithPublic)

Expand Down Expand Up @@ -709,10 +711,11 @@ var txnRowsReadErr = settings.RegisterIntSetting(
var largeFullScanRows = settings.RegisterFloatSetting(
settings.ApplicationLevel,
"sql.defaults.large_full_scan_rows",
"default value for large_full_scan_rows session setting which determines "+
"the maximum table size allowed for a full scan when disallow_full_table_scans "+
"is set to true",
1000.0,
"default value for large_full_scan_rows session variable which determines "+
"the table size at which full scans are considered large and disallowed "+
"when disallow_full_table_scans is set to true; set to 0 to reject all "+
"full table or full index scans when disallow_full_table_scans is true",
0,
settings.WithPublic)

var costScansWithDefaultColSize = settings.RegisterBoolSetting(
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2 changes: 1 addition & 1 deletion pkg/sql/logictest/testdata/logic_test/information_schema
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Original file line number Diff line number Diff line change
Expand Up @@ -6273,7 +6273,7 @@ is_superuser on
join_reader_index_join_strategy_batch_size 4.0 MiB
join_reader_no_ordering_strategy_batch_size 2.0 MiB
join_reader_ordering_strategy_batch_size 100 KiB
large_full_scan_rows 1000
large_full_scan_rows 0
lc_collate C.UTF-8
lc_ctype C.UTF-8
lc_messages C.UTF-8
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4 changes: 2 additions & 2 deletions pkg/sql/logictest/testdata/logic_test/pg_catalog
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Original file line number Diff line number Diff line change
Expand Up @@ -2918,7 +2918,7 @@ is_superuser on N
join_reader_index_join_strategy_batch_size 4.0 MiB NULL NULL NULL string
join_reader_no_ordering_strategy_batch_size 2.0 MiB NULL NULL NULL string
join_reader_ordering_strategy_batch_size 100 KiB NULL NULL NULL string
large_full_scan_rows 1000 NULL NULL NULL string
large_full_scan_rows 0 NULL NULL NULL string
lc_collate C.UTF-8 NULL NULL NULL string
lc_ctype C.UTF-8 NULL NULL NULL string
lc_messages C.UTF-8 NULL NULL NULL string
Expand Down Expand Up @@ -3110,7 +3110,7 @@ is_superuser on N
join_reader_index_join_strategy_batch_size 4.0 MiB NULL user NULL 4.0 MiB 4.0 MiB
join_reader_no_ordering_strategy_batch_size 2.0 MiB NULL user NULL 2.0 MiB 2.0 MiB
join_reader_ordering_strategy_batch_size 100 KiB NULL user NULL 100 KiB 100 KiB
large_full_scan_rows 1000 NULL user NULL 1000 1000
large_full_scan_rows 0 NULL user NULL 0 0
lc_collate C.UTF-8 NULL user NULL C.UTF-8 C.UTF-8
lc_ctype C.UTF-8 NULL user NULL C.UTF-8 C.UTF-8
lc_messages C.UTF-8 NULL user NULL C.UTF-8 C.UTF-8
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2 changes: 1 addition & 1 deletion pkg/sql/logictest/testdata/logic_test/show_source
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Original file line number Diff line number Diff line change
Expand Up @@ -105,7 +105,7 @@ is_superuser on
join_reader_index_join_strategy_batch_size 4.0 MiB
join_reader_no_ordering_strategy_batch_size 2.0 MiB
join_reader_ordering_strategy_batch_size 100 KiB
large_full_scan_rows 1000
large_full_scan_rows 0
lc_collate C.UTF-8
lc_ctype C.UTF-8
lc_messages C.UTF-8
Expand Down
2 changes: 1 addition & 1 deletion pkg/sql/opt/exec/execbuilder/relational.go
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Original file line number Diff line number Diff line change
Expand Up @@ -770,7 +770,7 @@ func (b *Builder) buildScan(scan *memo.ScanExpr) (_ execPlan, outputCols colOrdM
relProps := scan.Relational()
stats := relProps.Statistics()
if !tab.IsVirtualTable() && isUnfiltered {
large := !stats.Available || stats.RowCount > b.evalCtx.SessionData().LargeFullScanRows
large := !stats.Available || stats.RowCount >= b.evalCtx.SessionData().LargeFullScanRows
if scan.Index == cat.PrimaryIndex {
b.flags.Set(exec.PlanFlagContainsFullTableScan)
if large {
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