THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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- The following settings are required in hive-site.xml to enable ACID support for streaming:
- “stored as orc” must be specified during table creation. Only ORC storage format is supported currently.
- tblproperties("transactional"="true") must be set on the table during creation.
User of the client streaming process must have the necessary permissions to write to the table or partition and create partitions in the table.
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Generally, the more records are included in each transaction the more throughput can be achieved. It's common to commit either after a certain number of records or after a certain time interval, whichever comes first. The later ensures that when event flow rate is variable, transactions don't stay open too long. There is no practical limit on how much data can be included in a single transaction. The The only concern is amount of data which will need to be replayed if the transaction fails. The The concept of a TransactionBatch serves to reduce the number of files (and delta directories) created by HiveStreamingConnection API in the filesystem. Since all transactions in a given transaction batch write to the same physical file (per bucket), a partition can only be compacted up to the the level of the earliest transaction of any batch which contains an open transaction. Thus TransactionBatches should not be made excessively large. It makes sense to include a timer to close a TransactionBatch (even if it has unused transactions) after some amount of time.
Notes about the HiveConf Object
The HiveStreamingConnection is highly optimized for write throughput (Delta Streaming Optimizations) and as a result the delta files generated by Hive streaming ingest have many of the ORC features disabled (dictionary encoding, indexes, compression, etc.) to facilitate high throughput writes. When the compactor kicks in, these delta files get rewritten into read- and storage-optimized ORC format (enable dictionary encoding, indexes and compression). So it is recommended to configure the compactor more aggressively/frequently (refer to Compactor) to generate compacted and optimized ORC files.
Notes about the HiveConf Object
HiveStreamingConnect builder API accepts a HiveStreamingConnect builder API accepts a HiveConf argument. This can either be set to null, or a pre-created HiveConf object can be provided. If this is null, a HiveConf object will be created internally and used for the connection. When a HiveConf object is instantiated, if the directory containing the hive-site.xml is part of the java classpath, then the HiveConf object will be initialized with values from it. If no hive-site.xml is found, then the object will be initialized with defaults. Pre-creating this object and reusing it across multiple connections may have a noticeable impact on performance if connections are being opened very frequently (for example several times a second). Secure connection relies on 'metastore.kerberos.principal' being set correctly in the HiveConf object.
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- hive.txn.manager = org.apache.hadoop.hive.ql.lockmgr.DbTxnManager
- hive.support.concurrency = true
- hive.metastore.execute.setugi = truehive.execution.engine = mr
- hive.exec.dynamic.partition.mode = nonstrict
- hive.exec.orc.delta.streaming.optimizations.enabled = true
- hive.metastore.client.cache.enabled = false
I/O – Writing Data
These classes and interfaces provide support for writing the data to Hive within a transaction.
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- Modify input record: This may involve dropping fields from input data if they don’t have corresponding table columns, adding nulls in case of missing fields for certain columns, and adding __HIVE_DEFAULT_PARTITION__ if partition column value is null or empty. Dynamically creating partitions requires understanding of incoming data format to extract last columns to extract partition values.
- Encode modified record: The encoding involves serialization using an appropriate Hive SerDe.
- Identify For bucketed tables, extract bucket column values from the record to identify the bucket to which where the record belongsIdentify the partition to which .
- For partitioned tables, in dynamic partitioning mode, extract the partition column values from last N columns (where N is number of partitions) of the record to identify the partition where the record belongs.
- Write encoded record to Hive using the AcidOutputFormat's record updater for the appropriate bucket.
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