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https://issues.apache.org/jira/browse/TS-4331?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15304220#comment-15304220
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ASF GitHub Bot commented on TS-4331:
------------------------------------
Github user jpeach commented on a diff in the pull request:
https://github.com/apache/trafficserver/pull/653#discussion_r64925841
--- Diff: iocore/hostdb/P_RefCountCache.h ---
@@ -0,0 +1,572 @@
+#ifndef _P_RefCountCache_h_
+#define _P_RefCountCache_h_
+
+#include "I_EventSystem.h"
+
+#include <ts/Map.h>
+#include <ts/List.h>
+
+#include <cstdint>
+// TODO: no vector?
+#include <vector>
+#include <unistd.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <cmath>
+#include <fstream>
+
+#include "ts/I_Version.h"
+
+#define REFCOUNT_CACHE_EVENT_SYNC REFCOUNT_CACHE_EVENT_EVENTS_START
+
+#define REFCOUNTCACHE_MAGIC_NUMBER 0x0BAD2D9
+#define REFCOUNTCACHE_MAJOR_VERSION 1
+#define REFCOUNTCACHE_MINOR_VERSION 0
+
+// TODO: elsewhere?
+#define PtrMutex Ptr<ProxyMutex>
+
+// In the cache we want to recount our items
+// This class will handle memory allocations (on the freelist) and
+// take care of implementing RefCountObj-- so that the items we want in
+// the cache don't have to inherit from it (which makes
serialization/deserialization much easier)
+class RefCountCacheItemBase : public RefCountObj
--- End diff --
The STL design pattern is to associate the allocator with the container. In
this approach knowledge of the allocator is distributed across the container
and the contained objects. It would be much better to isolate this and have the
container return Ptr<C> directly, hiding all the internal implementation
details.
> Hostdb consistency problems due to MultiCache
> ---------------------------------------------
>
> Key: TS-4331
> URL: https://issues.apache.org/jira/browse/TS-4331
> Project: Traffic Server
> Issue Type: Bug
> Components: HostDB
> Reporter: Thomas Jackson
> Assignee: Thomas Jackson
> Fix For: 7.0.0
>
>
> This ticket is for the correct long term fix to TS-4207
> pulled from a comment, which wraps up the issue
> {quote}
> Leif Hedstrom I have spent a decent amount of time on this while I was OOO on
> vacation the last couple of weeks. It seems that the root cause of this issue
> has always existed, and that the addition of always doing hostname storing
> (https://github.com/apache/trafficserver/commit/0e703e1e) we are just causing
> the issue to happen all the time.
> To understand the issue I'll give a little background in how hostdb is
> currently working. Basically hostdb is just a wrapper around this templated
> struct called MultiCache. MultiCache is "multi" not because it is templated,
> but because it has two types of storage (static-- blocks and dynamic--
> alloc). The static side of the cache can hold N HostDBInfo structs (the
> results of DNS queries). The dynamic side is used to store the round robin
> records and various strings associated with the record. The size of this
> dynamic space is defined as (N x [estimated_heap_bytes_per_entry. The basic
> problem we are running into is that we are putting too much preassure on the
> dynamic heap-- such that the heap is getting re-used while people still have
> references to items in that space.
> So, I've actually been working on re-writing MultiCache to allocate the
> entire required block at once (so we don't have this problem where the parent
> exists but not the children), but I'm not certain if we want such a change to
> go into the 6.x branch (I'm willing to discuss if we want). If we aren't
> comfortable with such a large change I suggest just accounting for the
> hostname size in the estimated_heap_bytes_per_entry as a stopgap solution.
> The maximum allowable size is 253 (so 254 with null terminator), but we could
> pick a smaller number (~120 or so seems to be more reasonable). Alternatively
> you can increase the number of records in hostdb (and the size accordingly)
> to increase the dynamic heap size.
> TLDR; almost done with the long term solution, but I'm not sure if we want to
> merge that into 6.x-- alternatively we can do a simple workaround in 6.x
> (https://github.com/apache/trafficserver/pull/553)
> {quote}
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