Re: Protect syscache from bloating with negative cache entries - Mailing list pgsql-hackers

At Thu, 28 Jan 2021 16:50:44 +0900 (JST), Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote in 
> I was going to write in the doc something like "you can inspect memory
> consumption by catalog caches using pg_backend_memory_contexts", but
> all the memory used by catalog cache is in CacheMemoryContext.  Is it
> sensible for each catalog cache to have their own contexts?

Something like this.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center
diff --git a/src/backend/utils/cache/catcache.c b/src/backend/utils/cache/catcache.c
index fa2b49c676..cfbb335bb3 100644
--- a/src/backend/utils/cache/catcache.c
+++ b/src/backend/utils/cache/catcache.c
@@ -769,6 +769,8 @@ InitCatCache(int id,
 {
     CatCache   *cp;
     MemoryContext oldcxt;
+    MemoryContext mycxt;
+    char        name[32];
     size_t        sz;
     int            i;
 
@@ -792,7 +794,12 @@ InitCatCache(int id,
     if (!CacheMemoryContext)
         CreateCacheMemoryContext();
 
-    oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
+    mycxt = AllocSetContextCreate(CacheMemoryContext, "catcache",
+                                  ALLOCSET_DEFAULT_SIZES);
+
+    snprintf(name, sizeof(name), "catcache id %d", id);
+    oldcxt = MemoryContextSwitchTo(mycxt);
+    MemoryContextSetIdentifier(mycxt, (const char *)pstrdup(name));
 
     /*
      * if first time through, initialize the cache group header
@@ -833,6 +840,7 @@ InitCatCache(int id,
     cp->cc_nkeys = nkeys;
     for (i = 0; i < nkeys; ++i)
         cp->cc_keyno[i] = key[i];
+    cp->cc_mcxt = mycxt;
 
     /*
      * new cache is initialized as far as we can go for now. print some
@@ -932,12 +940,12 @@ CatalogCacheInitializeCache(CatCache *cache)
     relation = table_open(cache->cc_reloid, AccessShareLock);
 
     /*
-     * switch to the cache context so our allocations do not vanish at the end
-     * of a transaction
+     * switch to our own context under the cache context so our allocations do
+     * not vanish at the end of a transaction
      */
     Assert(CacheMemoryContext != NULL);
 
-    oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
+    oldcxt = MemoryContextSwitchTo(cache->cc_mcxt);
 
     /*
      * copy the relcache's tuple descriptor to permanent cache storage
@@ -998,7 +1006,7 @@ CatalogCacheInitializeCache(CatCache *cache)
          */
         fmgr_info_cxt(eqfunc,
                       &cache->cc_skey[i].sk_func,
-                      CacheMemoryContext);
+                      cache->cc_mcxt);
 
         /* Initialize sk_attno suitably for HeapKeyTest() and heap scans */
         cache->cc_skey[i].sk_attno = cache->cc_keyno[i];
@@ -1697,7 +1705,7 @@ SearchCatCacheList(CatCache *cache,
         table_close(relation, AccessShareLock);
 
         /* Now we can build the CatCList entry. */
-        oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
+        oldcxt = MemoryContextSwitchTo(cache->cc_mcxt);
         nmembers = list_length(ctlist);
         cl = (CatCList *)
             palloc(offsetof(CatCList, members) + nmembers * sizeof(CatCTup *));
@@ -1830,7 +1838,7 @@ CatalogCacheCreateEntry(CatCache *cache, HeapTuple ntp, Datum *arguments,
             dtp = ntp;
 
         /* Allocate memory for CatCTup and the cached tuple in one go */
-        oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
+        oldcxt = MemoryContextSwitchTo(cache->cc_mcxt);
 
         ct = (CatCTup *) palloc(sizeof(CatCTup) +
                                 MAXIMUM_ALIGNOF + dtp->t_len);
@@ -1865,7 +1873,7 @@ CatalogCacheCreateEntry(CatCache *cache, HeapTuple ntp, Datum *arguments,
     else
     {
         Assert(negative);
-        oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
+        oldcxt = MemoryContextSwitchTo(cache->cc_mcxt);
         ct = (CatCTup *) palloc(sizeof(CatCTup));
 
         /*
diff --git a/src/include/utils/catcache.h b/src/include/utils/catcache.h
index ddc2762eb3..a32fea2f11 100644
--- a/src/include/utils/catcache.h
+++ b/src/include/utils/catcache.h
@@ -61,6 +61,7 @@ typedef struct catcache
     slist_node    cc_next;        /* list link */
     ScanKeyData cc_skey[CATCACHE_MAXKEYS];    /* precomputed key info for heap
                                              * scans */
+    MemoryContext    cc_mcxt;    /* memory context for this cache */
 
     /*
      * Keep these at the end, so that compiling catcache.c with CATCACHE_STATS