Repository: drill-site Updated Branches: refs/heads/asf-site 34faadd80 -> 0b2565cad
doc update for DRILL-3867 Project: http://git-wip-us.apache.org/repos/asf/drill-site/repo Commit: http://git-wip-us.apache.org/repos/asf/drill-site/commit/0b2565ca Tree: http://git-wip-us.apache.org/repos/asf/drill-site/tree/0b2565ca Diff: http://git-wip-us.apache.org/repos/asf/drill-site/diff/0b2565ca Branch: refs/heads/asf-site Commit: 0b2565cad2a37fe82b3b1db7ed4162526dd5bac8 Parents: 34faadd Author: Bridget Bevens <bbev...@maprtech.com> Authored: Thu Aug 10 15:31:14 2017 -0700 Committer: Bridget Bevens <bbev...@maprtech.com> Committed: Thu Aug 10 15:31:14 2017 -0700 ---------------------------------------------------------------------- .../index.html | 47 ++++++++++++-------- feed.xml | 4 +- 2 files changed, 31 insertions(+), 20 deletions(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/drill-site/blob/0b2565ca/docs/optimizing-parquet-metadata-reading/index.html ---------------------------------------------------------------------- diff --git a/docs/optimizing-parquet-metadata-reading/index.html b/docs/optimizing-parquet-metadata-reading/index.html index 6e38ecd..caa93cd 100644 --- a/docs/optimizing-parquet-metadata-reading/index.html +++ b/docs/optimizing-parquet-metadata-reading/index.html @@ -1124,40 +1124,51 @@ </div> - Feb 8, 2016 + Aug 10, 2017 <link href="/css/docpage.css" rel="stylesheet" type="text/css"> <div class="int_text" align="left"> - <p>Parquet metadata caching is an optional feature in Drill 1.2 and later. When you use this feature, Drill generates a metadata cache file. Drill stores the metadata cache file in a directory you specify and its subdirectories. When you run a query on this directory or a subdirectory, Drill reads a single metadata cache file instead of retrieving metadata from multiple Parquet files during the query-planning phase.</p> + <p>Parquet metadata caching is a feature that enables Drill to read a single metadata cache file instead of retrieving metadata from multiple Parquet files during the query-planning phase. +Parquet metadata caching is available for Parquet data in Drill 1.2 and later. To enable Parquet metadata caching, issue the REFRESH TABLE METADATA <path to table> command. When you run this command Drill generates a metadata cache file. </p> -<p>Parquet metadata caching is useful only with Parquet data, and does not benefit queries on Hive tables, HBase tables, or text files. </p> +<div class="admonition note"> + <p class="first admonition-title">Note</p> + <p class="last">Parquet metadata caching does not benefit queries on Hive tables, HBase tables, or text files. </p> +</div> + +<p>Drill stores the metadata cache file in the specified directory and subdirectories. When you run a query on this directory or subdirectories, Drill reads the metadata cache file instead of retrieving metadata from multiple Parquet files during the query-planning phase. </p> + +<p>In Drill 1.11 and later, Drill stores the paths to the Parquet files as relative paths instead of absolute paths. You can move partitioned Parquet directories from one location in the distributed files system to another without issuing the REFRESH TABLE METADATA command to rebuild the Parquet metadata files; the metadata remains valid in the new location. </p> + +<div class="admonition note"> + <p class="first admonition-title">Note</p> + <p class="last">Reverting back to a previous version of Drill from 1.11 is not recommended because Drill will incorrectly interpret the Parquet metadata files created by Drill 1.11. Should this occur, remove the Parquet metadata files and run the refresh table metadata command to rebuild the files in the older format. </p> +</div> + <h2 id="when-to-use-parquet-metadata-caching">When to Use Parquet Metadata Caching</h2> -<p>The scenarios in which metadata caching is useful is when the planning time is a significant percentage of the total elapsed time of the query. If the query execution time is the dominant factor, which is typically observed with a large number of files, then metadata caching will have very little impact. To determine that query execution time is the dominant factor, run an EXPLAIN plan on your query of a large number of files, and compare its time to the total time of query execution. Use the comparison to determine whether metadata caching will be useful.</p> +<p>Metadata caching is useful when planning time is a significant percentage of the total elapsed time of the query. If the query execution time is the dominant factor, which is typically observed with a large number of files, then metadata caching will have very little impact. To determine that query execution time is the dominant factor, run an EXPLAIN plan on your query of a large number of files, and compare its time to the total time of query execution. Use the comparison to determine whether metadata caching will be useful.</p> <p>When enabled, Drill always uses the Parquet metadata cache during the query-planning phase. To optimize reading Parquet metadata, make sure the metadata cache is up-to-date after making any changes, such as inserts, to the data in the cluster. The next section describes how to update the metadata cache.</p> -<h2 id="how-to-trigger-generation-of-the-parquet-metadata-cache-file">How to Trigger Generation of the Parquet Metadata Cache File</h2> +<h2 id="generating-the-parquet-metadata-cache-file">Generating the Parquet Metadata Cache File</h2> <p>The following command generates the Parquet metadata cache file in the <code><path to table></code> and its subdirectories.</p> - -<p><code>REFRESH TABLE METADATA <path to table></code></p> - +<div class="highlight"><pre><code class="language-text" data-lang="text"> REFRESH TABLE METADATA <path to table> +</code></pre></div> <p>You need to run this command on a directory, nested or flat, only once during the session. Only the first query gathers the metadata unless the Parquet data changes, for example, you delete some data. If you did not make changes to the Parquet data, subsequent queries encounter the up-to-date Parquet metadata files. There is no need for Drill to regenerate the metadata. If there are changes, the metadata needs updating, so Drill dynamically regenerates the Parquet metadata when you issue the next query.</p> -<p>The elapsed time of the first query that triggers regeneration of metadata can be greater than that of subsequent queries that use that metadata. If this increase in the time of the first query is unacceptable, make sure the cache is up-to-date by running the REFRESH TABLE METADATA command.</p> - -<h2 id="example-of-generating-parquet-metadata">Example of Generating Parquet Metadata</h2> -<div class="highlight"><pre><code class="language-text" data-lang="text">0: jdbc:drill:schema=dfs> REFRESH TABLE METADATA t1; -+-------+----------------------------------------------+ -| ok | summary | -+-------+----------------------------------------------+ -| true | Successfully updated metadata for table t1. | -+-------+----------------------------------------------+ -1 row selected (0.445 seconds) +<p>The elapsed time of the first query that triggers regeneration of metadata can be greater than that of subsequent queries that use that metadata. If this increase in the time of the first query is unacceptable, make sure the cache is up-to-date by running the REFRESH TABLE METADATA command, as shown in the following example:</p> +<div class="highlight"><pre><code class="language-text" data-lang="text"> 0: jdbc:drill:schema=dfs> REFRESH TABLE METADATA t1; + +-------+----------------------------------------------+ + | ok | summary | + +-------+----------------------------------------------+ + | true | Successfully updated metadata for table t1. | + +-------+----------------------------------------------+ + 1 row selected (0.445 seconds) </code></pre></div> <h2 id="how-drill-generates-and-uses-parquet-metadata">How Drill Generates and Uses Parquet Metadata</h2> http://git-wip-us.apache.org/repos/asf/drill-site/blob/0b2565ca/feed.xml ---------------------------------------------------------------------- diff --git a/feed.xml b/feed.xml index a74c616..9b92428 100644 --- a/feed.xml +++ b/feed.xml @@ -6,8 +6,8 @@ </description> <link>/</link> <atom:link href="/feed.xml" rel="self" type="application/rss+xml"/> - <pubDate>Wed, 09 Aug 2017 16:02:54 -0700</pubDate> - <lastBuildDate>Wed, 09 Aug 2017 16:02:54 -0700</lastBuildDate> + <pubDate>Thu, 10 Aug 2017 15:27:39 -0700</pubDate> + <lastBuildDate>Thu, 10 Aug 2017 15:27:39 -0700</lastBuildDate> <generator>Jekyll v2.5.2</generator> <item>
