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Commit2c300c6

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Be smarter about age-counter overflow in formatting.c caches.
The previous code here simply threw away whatever it knew about cacheentry ages whenever a counter overflow occurred. Since the counteris int width and will be bumped once per format function execution,overflows are not really so rare as to not be worth thinking about.Instead, let's deal with the situation by halving all the age values,essentially rescaling the age metric. In that way, we retain apretty accurate (if not quite perfect) idea of which entries are oldest.
1 parentf7a953c commit2c300c6

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+38
-32
lines changed

1 file changed

+38
-32
lines changed

‎src/backend/utils/adt/formatting.c

Lines changed: 38 additions & 32 deletions
Original file line numberDiff line numberDiff line change
@@ -3376,20 +3376,32 @@ DCH_from_char(FormatNode *node, char *in, TmFromChar *out)
33763376
}
33773377
}
33783378

3379+
/*
3380+
* The invariant for DCH cache entry management is that DCHCounter is equal
3381+
* to the maximum age value among the existing entries, and we increment it
3382+
* whenever an access occurs. If we approach overflow, deal with that by
3383+
* halving all the age values, so that we retain a fairly accurate idea of
3384+
* which entries are oldest.
3385+
*/
3386+
staticinlinevoid
3387+
DCH_prevent_counter_overflow(void)
3388+
{
3389+
if (DCHCounter >= (INT_MAX-1))
3390+
{
3391+
for (inti=0;i<n_DCHCache;i++)
3392+
DCHCache[i]->age >>=1;
3393+
DCHCounter >>=1;
3394+
}
3395+
}
3396+
33793397
/* select a DCHCacheEntry to hold the given format picture */
33803398
staticDCHCacheEntry*
33813399
DCH_cache_getnew(constchar*str)
33823400
{
33833401
DCHCacheEntry*ent;
33843402

3385-
/* handle counter overflow by resetting all ages */
3386-
if (DCHCounter >= (INT_MAX-DCH_CACHE_ENTRIES))
3387-
{
3388-
DCHCounter=0;
3389-
3390-
for (inti=0;i<n_DCHCache;i++)
3391-
DCHCache[i]->age= (++DCHCounter);
3392-
}
3403+
/* Ensure we can advance DCHCounter below */
3404+
DCH_prevent_counter_overflow();
33933405

33943406
/*
33953407
* If cache is full, remove oldest entry (or recycle first not-valid one)
@@ -3445,14 +3457,8 @@ DCH_cache_getnew(const char *str)
34453457
staticDCHCacheEntry*
34463458
DCH_cache_search(constchar*str)
34473459
{
3448-
/* handle counter overflow by resetting all ages */
3449-
if (DCHCounter >= (INT_MAX-DCH_CACHE_ENTRIES))
3450-
{
3451-
DCHCounter=0;
3452-
3453-
for (inti=0;i<n_DCHCache;i++)
3454-
DCHCache[i]->age= (++DCHCounter);
3455-
}
3460+
/* Ensure we can advance DCHCounter below */
3461+
DCH_prevent_counter_overflow();
34563462

34573463
for (inti=0;i<n_DCHCache;i++)
34583464
{
@@ -4057,20 +4063,26 @@ do { \
40574063
(_n)->zero_end= 0;\
40584064
} while(0)
40594065

4066+
/* This works the same as DCH_prevent_counter_overflow */
4067+
staticinlinevoid
4068+
NUM_prevent_counter_overflow(void)
4069+
{
4070+
if (NUMCounter >= (INT_MAX-1))
4071+
{
4072+
for (inti=0;i<n_NUMCache;i++)
4073+
NUMCache[i]->age >>=1;
4074+
NUMCounter >>=1;
4075+
}
4076+
}
4077+
40604078
/* select a NUMCacheEntry to hold the given format picture */
40614079
staticNUMCacheEntry*
40624080
NUM_cache_getnew(constchar*str)
40634081
{
40644082
NUMCacheEntry*ent;
40654083

4066-
/* handle counter overflow by resetting all ages */
4067-
if (NUMCounter >= (INT_MAX-NUM_CACHE_ENTRIES))
4068-
{
4069-
NUMCounter=0;
4070-
4071-
for (inti=0;i<n_NUMCache;i++)
4072-
NUMCache[i]->age= (++NUMCounter);
4073-
}
4084+
/* Ensure we can advance NUMCounter below */
4085+
NUM_prevent_counter_overflow();
40744086

40754087
/*
40764088
* If cache is full, remove oldest entry (or recycle first not-valid one)
@@ -4126,14 +4138,8 @@ NUM_cache_getnew(const char *str)
41264138
staticNUMCacheEntry*
41274139
NUM_cache_search(constchar*str)
41284140
{
4129-
/* handle counter overflow by resetting all ages */
4130-
if (NUMCounter >= (INT_MAX-NUM_CACHE_ENTRIES))
4131-
{
4132-
NUMCounter=0;
4133-
4134-
for (inti=0;i<n_NUMCache;i++)
4135-
NUMCache[i]->age= (++NUMCounter);
4136-
}
4141+
/* Ensure we can advance NUMCounter below */
4142+
NUM_prevent_counter_overflow();
41374143

41384144
for (inti=0;i<n_NUMCache;i++)
41394145
{

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