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Replace the sorted array of GUC variables with a hash table.

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This gets rid of bsearch() in favor of hashed lookup.  The main
advantage is that it becomes far cheaper to add new GUCs, since
we needn't re-sort the pointer array.  Adding N new GUCs had
been O(N^2 log N), but now it's closer to O(N).  We need to
sort only in SHOW ALL and equivalent functions, which are
hopefully not performance-critical to anybody.

Also, merge GetNumConfigOptions() into get_guc_variables(),
because in a world where the set of GUCs isn't fairly static
you really want to consider those two results as tied together
not independent.

Discussion: https://postgr.es/m/2982579.1662416866@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2022-10-14 12:26:39 -04:00
parent 407b50f2d4
commit 3057465acf
5 changed files with 272 additions and 160 deletions
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39
src/backend/utils/misc/guc_funcs.c
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@@ -455,13 +455,15 @@ ShowGUCConfigOption(const char *name, DestReceiver *dest)
static void
ShowAllGUCConfig(DestReceiver *dest)
{
int i;
struct config_generic **guc_vars;
int num_vars;
TupOutputState *tstate;
TupleDesc tupdesc;
Datum values[3];
bool isnull[3] = {false, false, false};
struct config_generic **guc_variables = get_guc_variables();
int num_guc_variables = GetNumConfigOptions();
/* collect the variables, in sorted order */
guc_vars = get_guc_variables(&num_vars);
/* need a tuple descriptor representing three TEXT columns */
tupdesc = CreateTemplateTupleDesc(3);
@@ -475,9 +477,9 @@ ShowAllGUCConfig(DestReceiver *dest)
/* prepare for projection of tuples */
tstate = begin_tup_output_tupdesc(dest, tupdesc, &TTSOpsVirtual);
for (i = 0; i < num_guc_variables; i++)
for (int i = 0; i < num_vars; i++)
{
struct config_generic *conf = guc_variables[i];
struct config_generic *conf = guc_vars[i];
char *setting;
if ((conf->flags & GUC_NO_SHOW_ALL) ||
@@ -570,20 +572,13 @@ pg_settings_get_flags(PG_FUNCTION_ARGS)
}
/*
* Return GUC variable value by variable number; optionally return canonical
* form of name. Return value is palloc'd.
* Extract fields to show in pg_settings for given variable.
*/
static void
GetConfigOptionByNum(int varnum, const char **values, bool *noshow)
GetConfigOptionValues(struct config_generic *conf, const char **values,
bool *noshow)
{
char buffer[256];
struct config_generic *conf;
struct config_generic **guc_variables = get_guc_variables();
/* check requested variable number valid */
Assert((varnum >= 0) && (varnum < GetNumConfigOptions()));
conf = guc_variables[varnum];
if (noshow)
{
@@ -849,6 +844,8 @@ Datum
show_all_settings(PG_FUNCTION_ARGS)
{
FuncCallContext *funcctx;
struct config_generic **guc_vars;
int num_vars;
TupleDesc tupdesc;
int call_cntr;
int max_calls;
@@ -913,8 +910,14 @@ show_all_settings(PG_FUNCTION_ARGS)
attinmeta = TupleDescGetAttInMetadata(tupdesc);
funcctx->attinmeta = attinmeta;
/* collect the variables, in sorted order */
guc_vars = get_guc_variables(&num_vars);
/* use user_fctx to remember the array location */
funcctx->user_fctx = guc_vars;
/* total number of tuples to be returned */
funcctx->max_calls = GetNumConfigOptions();
funcctx->max_calls = num_vars;
MemoryContextSwitchTo(oldcontext);
}
@@ -922,6 +925,7 @@ show_all_settings(PG_FUNCTION_ARGS)
/* stuff done on every call of the function */
funcctx = SRF_PERCALL_SETUP();
guc_vars = (struct config_generic **) funcctx->user_fctx;
call_cntr = funcctx->call_cntr;
max_calls = funcctx->max_calls;
attinmeta = funcctx->attinmeta;
@@ -938,7 +942,8 @@ show_all_settings(PG_FUNCTION_ARGS)
*/
do
{
GetConfigOptionByNum(call_cntr, (const char **) values, &noshow);
GetConfigOptionValues(guc_vars[call_cntr], (const char **) values,
&noshow);
if (noshow)
{
/* bump the counter and get the next config setting */