Hey, On 29 November 2017 at 11:12, Antoni Ivanov <[email protected]> wrote: > Thanks, > I hope you don't mind a few more questions: > >> Node2 would also eventually consider these invalidated > - How exactly does it work. E.g When I issue invalidate metadata. Does it say > to the catalogd to invalidate metadata or is this information broadcasted > through the statestored?
That's right, it's invalidated on the catalogd first, then propagated to the daemons through statestore. >> stored in the catalog daemon centrally > - Oh so metadata is stored in the catalogD . I thought it was stored only in > the statestore (and cached in each ImpalaD) and catalog facilitate fetching > metadata from Hive Metastore and Block information from HDFS Namenode. > What was I wrong ? Statestore is only responsible for pushing the catalog changes to the impala daemons, catalogd is the central store. I'm not 100% sure about how the catalog deltas are stored in the statestore so I'll let others comment. > - Does INVALIDATE METADATA have any impact on the Hive Metastore . I don't > believe so, right? E.g instead of running invalidate metadata (say after HDFS > rebalance) I can restart Impala to clear caches (including statestore catalog > topic) so that new data is loaded lazily again. A global 'invalidate metadata' (i.e. not a table-specific one) will have the same impact on the HMS as a catalog / service restart would. Impala will have to fetch a list of tables in both cases, so there is some work on the HMS side, but it's miniscule. It matters when HMS is unreachable, for example. One addition, I just noticed that earlier you said that most of the 2000 tables have much less partitions than 5000, so YMMV. Partition and file count will directly impact metadata size, the less you have, the better (metadata-wise, at least). Regards > -Antoni > > -----Original Message----- > From: Jeszy [mailto:[email protected]] > Sent: Wednesday, November 29, 2017 9:56 AM > To: [email protected] > Cc: [email protected] > Subject: Re: invalidate metadata behaviour > > Hey Antoni, > > On 29 November 2017 at 07:42, Antoni Ivanov <[email protected]> wrote: >> Hi, >> >> >> >> I am wondering if I run INVALIDATE METADATA for the whole database on >> node1 >> >> Then I ran a query on node2 – would the query on node2 used the cached >> metadata for the tables or it would know it’s invalidated? > > Node2 would also eventually consider these invalidated. > >> And second how safe it is to run it for a database with many (say 30) >> tables over 10,000 partitions and 2000 more under 5000 partitions >> (most of the under 100) >> >> And each Impala Deamon node has a little (below Cloudera recommended) >> memory >> (32G) > > These numbers influence the size of the catalog cache, which is stored in the > catalog daemon centrally, and then replicated on each impalad, or on each > coordinator in more recent versions. The metadata you mention (2000 tables * > 5000 partitions each, plus the big tables) is in the 10 million partitions > range. Each of those will have at least one file with 3 blocks, probably > more, so all this adds up to a sizeable metadata. The cached version will > require a large amount of memory (on the catalog as well as the > daemons/coordinators), which could easily lead to even small queries running > out of memory with only 32gb. > >> Thanks, >> >> Antoni > > HTH
