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Accept invalidation messages before accessing the metadata cache 

This commit is crucial to prevent stale metadata reads from the
cache. Without this commit, some of the operations may use stale
metadata which could end up with various bugs such as crashes,
inconsistent/lost data etc.

As an example, consider that a COPY operation is blocked on shard
metadata lock. Another concurrent session updates the metadata and
invalidates the cache. However, since Citus doesn't accept invalidations,
COPY continues with the stale metadata once it acquires the lock.

With this commit, we make sure that invalidation messages are accepted
just before accessing the metadata cache and preventing any operation to
use stale metadata.
pull/1406/head
Onder Kalaci 2017-05-10 12:15:16 +03:00
parent 94151c9aef
commit 88ddde79f2
1 changed files with 26 additions and 5 deletions
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23
src/backend/distributed/utils/metadata_cache.c
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@ -385,7 +385,15 @@ LookupShardCacheEntry(int64 shardId)
recheck = true;
}
else if (!shardEntry->tableEntry->isValid)
else
{
/*
* We might have some concurrent metadata changes. In order to get the changes,
* we first need to accept the cache invalidation messages.
*/
AcceptInvalidationMessages();
if (!shardEntry->tableEntry->isValid)
{
/*
* The cache entry might not be valid right now. Reload cache entry
@ -394,6 +402,7 @@ LookupShardCacheEntry(int64 shardId)
LookupDistTableCacheEntry(shardEntry->tableEntry->relationId);
recheck = true;
}
}
/*
* If we (re-)loaded the table cache, re-search the shard cache - the
@ -472,6 +481,12 @@ LookupDistTableCacheEntry(Oid relationId)
/* return valid matches */
if (foundInCache)
{
/*
* We might have some concurrent metadata changes. In order to get the changes,
* we first need to accept the cache invalidation messages.
*/
AcceptInvalidationMessages();
if (cacheEntry->isValid)
{
return cacheEntry;
@ -1927,6 +1942,12 @@ InitializeDistTableCache(void)
HTAB *
GetWorkerNodeHash(void)
{
/*
* We might have some concurrent metadata changes. In order to get the changes,
* we first need to accept the cache invalidation messages.
*/
AcceptInvalidationMessages();
if (!workerNodeHashValid)
{
InitializeWorkerNodeCache();