8000 DEBUG: Add skip scan disable GUCs. · petergeoghegan/postgres@41599a7 · GitHub
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DEBUG: Add skip scan disable GUCs.
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‎src/backend/access/nbtree/nbtpreprocesskeys.c

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Original file line numberDiff line numberDiff line change
@@ -21,6 +21,33 @@
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#include "utils/lsyscache.h"
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#include "utils/memutils.h"
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/*
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* GUC parameters (temporary convenience for reviewers).
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*
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* To disable all skipping, set skipscan_prefix_cols=0. Otherwise set it to
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* the attribute number that you wish to make the last attribute number that
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* we can add a skip scan key for. For example, skipscan_prefix_cols=1 makes
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* an index scan with qual "WHERE b = 1 AND d = 42" generate a skip scan key
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* on the column 'a' (which is attnum 1) only, preventing us from adding one
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* for the column 'c'. And so only the scan key on 'b' (not the one on 'd')
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* gets marked required within _bt_preprocess_keys -- there is no 'c' skip
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* array to "anchor the required-ness" of 'b' through 'c' into 'd'.
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*/
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int skipscan_prefix_cols = INDEX_MAX_KEYS;
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/*
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* skipscan_skipsupport_enabled can be used to avoid using skip support. Used
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* to quantify the performance benefit that comes from having dedicated skip
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* support, with a given opclass and test query.
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*/
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bool skipscan_skipsupport_enabled = true;
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/*
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* skipscan_iprefix_enabled can be used to disable optimizations used when the
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* maintenance overhead of skip arrays stops paying for itself
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*/
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bool skipscan_iprefix_enabled = true;
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typedef struct BTScanKeyPreproc
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{
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ScanKey inkey;
@@ -1651,6 +1678,10 @@ _bt_preprocess_array_keys(IndexScanDesc scan, int *new_numberOfKeys)
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so->arrayKeys[numArrayKeys].low_compare = NULL; /* for now */
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so->arrayKeys[numArrayKeys].high_compare = NULL; /* for now */
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/* Temporary testing GUC can disable the use of skip support */
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if (!skipscan_skipsupport_enabled)
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so->arrayKeys[numArrayKeys].sksup = NULL;
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/*
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* We'll need a 3-way ORDER proc. Set that up now.
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*/
@@ -2177,6 +2208,12 @@ _bt_num_array_keys(IndexScanDesc scan, Oid *skip_eq_ops_out,
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if (attno_has_rowcompare)
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break;
21792210

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/*
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* Apply temporary testing GUC that can be used to disable skipping
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*/
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if (attno_inkey > skipscan_prefix_cols)
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break;
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/*
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* Now consider next attno_inkey (or keep going if this is an
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* additional scan key against the same attribute)

‎src/backend/access/nbtree/nbtutils.c

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Original file line numberDiff line numberDiff line change
@@ -2523,6 +2523,9 @@ _bt_set_startikey(IndexScanDesc scan, BTReadPageState *pstate)
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if (so->numberOfKeys == 0)
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return;
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if (!skipscan_iprefix_enabled)
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return;
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/* minoff is an offset to the lowest non-pivot tuple on the page */
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iid = PageGetItemId(pstate->page, pstate->minoff);
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firsttup = (IndexTuple) PageGetItem(pstate->page, iid);

‎src/backend/utils/misc/guc_tables.c

Lines changed: 34 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -31,6 +31,7 @@
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#include "access/commit_ts.h"
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#include "access/gin.h"
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#include "access/nbtree.h"
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#include "access/slru.h"
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#include "access/toast_compression.h"
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#include "access/twophase.h"
@@ -1800,6 +1801,28 @@ struct config_bool ConfigureNamesBool[] =
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},
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#endif
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/* XXX Remove before commit */
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{
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{"skipscan_skipsupport_enabled", PGC_SUSET, DEVELOPER_OPTIONS,
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NULL, NULL,
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GUC_NOT_IN_SAMPLE
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},
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&skipscan_skipsupport_enabled,
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true,
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NULL, NULL, NULL
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},
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/* XXX Remove before commit */
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{
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{"skipscan_iprefix_enabled", PGC_SUSET, DEVELOPER_OPTIONS,
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NULL, NULL,
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GUC_NOT_IN_SAMPLE
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},
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&skipscan_iprefix_enabled,
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true,
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NULL, NULL, NULL
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},
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18031826
{
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{"integer_datetimes", PGC_INTERNAL, PRESET_OPTIONS,
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gettext_noop("Shows whether datetimes are integer based."),
@@ -3736,6 +3759,17 @@ struct config_int ConfigureNamesInt[] =
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NULL, NULL, NULL
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},
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/* XXX Remove before commit */
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{
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{"skipscan_prefix_cols", PGC_SUSET, DEVELOPER_OPTIONS,
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NULL, NULL,
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GUC_NOT_IN_SAMPLE
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},
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&skipscan_prefix_cols,
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INDEX_MAX_KEYS, 0, INDEX_MAX_KEYS,
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NULL, NULL, NULL
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},
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{
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/* Can't be set in postgresql.conf */
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{"server_version_num", PGC_INTERNAL, PRESET_OPTIONS,

‎src/include/access/nbtree.h

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Original file line numberDiff line numberDiff line change
@@ -1179,6 +1179,11 @@ typedef struct BTOptions
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#define PROGRESS_BTREE_PHASE_PERFORMSORT_2 4
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#define PROGRESS_BTREE_PHASE_LEAF_LOAD 5
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1182+
/* GUC parameters (just a temporary convenience for reviewers) */
1183+
extern PGDLLIMPORT int skipscan_prefix_cols;
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extern PGDLLIMPORT bool skipscan_skipsupport_enabled;
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extern PGDLLIMPORT bool skipscan_iprefix_enabled;
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/*
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* external entry points for btree, in nbtree.c
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*/

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