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https://issues.apache.org/jira/browse/TS-4331?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15328903#comment-15328903
]
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_r66907362
--- Diff: iocore/hostdb/I_HostDBProcessor.h ---
@@ -139,10 +141,62 @@ struct SRVInfo {
unsigned int key;
};
-struct HostDBInfo {
+struct HostDBInfo : public RefCountObj {
/** Internal IP address data.
This is at least large enough to hold an IPv6 address.
*/
+
+ int iobuffer_index;
+ static HostDBInfo *
+ alloc(int size = 0)
+ {
+ size += sizeof(HostDBInfo);
+ int iobuffer_index = iobuffer_size_to_index(size);
+ ink_release_assert(iobuffer_index >= 0);
+ void *ptr = ioBufAllocator[iobuffer_index].alloc_void();
+ memset(ptr, 0, size);
+ HostDBInfo *ret = new (ptr) HostDBInfo();
+ ret->iobuffer_index = iobuffer_index;
+ return ret;
+ }
+
+ void
+ free()
+ {
+ ioBufAllocator[iobuffer_index].free_void((void *)(this));
+ }
+
+ // return a version number-- so we can manage compatibility with the
marshal/unmarshal
+ static VersionNumber
+ version()
+ {
+ return VersionNumber(1, 0);
+ }
+
+ static HostDBInfo *
+ unmarshall(char *buf, unsigned int size)
+ {
+ if (size < sizeof(HostDBInfo)) {
+ return NULL;
+ }
+ HostDBInfo *ret = HostDBInfo::alloc(size - sizeof(HostDBInfo));
+ int buf_index = ret->iobuffer_index;
+ memcpy((void *)ret, buf, size);
+ // Reset the refcount back to 0, this is a bit ugly-- but I'm not sure
we want to expose a method
+ // to mess with the refcount, since this is a fairly unique use case
+ ret = new (ret) HostDBInfo();
--- End diff --
You allocated ``sizeof(HostDBInfo)`` less than the given size, then put a
``HostDBInfo`` into it after all? Can you comment what is going on there?
> 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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