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new a4acaa3 edits
a4acaa3 is described below
commit a4acaa3d3ef201193177e797ee3b1d4c755e0a5f
Author: Bridget Bevens <[email protected]>
AuthorDate: Thu Dec 20 18:24:08 2018 -0800
edits
---
.../index.html | 14 ++++++++------
feed.xml | 4 ++--
2 files changed, 10 insertions(+), 8 deletions(-)
diff --git
a/docs/sort-based-and-hash-based-memory-constrained-operators/index.html
b/docs/sort-based-and-hash-based-memory-constrained-operators/index.html
index d26cfb8..5258fe0 100644
--- a/docs/sort-based-and-hash-based-memory-constrained-operators/index.html
+++ b/docs/sort-based-and-hash-based-memory-constrained-operators/index.html
@@ -1293,7 +1293,7 @@
</div>
- Dec 19, 2018
+ Dec 21, 2018
<link href="/css/docpage.css" rel="stylesheet" type="text/css">
@@ -1308,7 +1308,7 @@
</ul>
<p>Drill only uses the External Sort operator to sort data. Drill uses the
Hash-Aggregate operator to aggregate data. Alternatively, Drill can sort the
data and then use the (lightweight) Streaming-Aggregate operator to aggregate
data.
-Drill uses the Hash-Join operator to join data. Drill 1.15 introduces
semi-join functionality inside the Hash-Join operator to improve query
performance. Semi-joins remove the distinct processing below the Hash-Join and
eliminate the overhead incurred from using a Hash Aggregate. Prior to Drill
1.15 (or when <a
href="/docs/sort-based-and-hash-based-memory-constrained-operators/#disabling-the-hash-operators">semi-join
functionality is disabled</a>), Drill uses a Distinct Hash Aggregate to [...]
+Drill uses the Hash-Join operator to join data. Drill 1.15 introduces
semi-join functionality inside the Hash-Join operator to improve query
performance. Semi-joins remove the distinct processing below the Hash-Join and
eliminate the overhead incurred from using a Hash Aggregate. Prior to Drill
1.15 (or when <a
href="/docs/sort-based-and-hash-based-memory-constrained-operators/#disabling-the-hash-operators">semi-join
functionality is disabled</a>), Drill used a Distinct Hash Aggregate to [...]
<p>The memory configuration in Drill is specified as the memory limit
per-query, per-node. The allocated memory is equally divided among all
instances of the spillable operators (per query on each node). The number of
instances is the number of spillable operators in the query plan multiplied by
the maximal degree of parallelism. The maximal degree of parallelism is the
number of minor fragments required to perform the work for each instance of a
spillable operator. When an instance of a [...]
@@ -1401,7 +1401,7 @@ Enables or disables hash aggregation; otherwise, Drill
does a sort-based aggrega
<li><p><strong>planner.enable_hashjoin</strong><br>
Enables or disables hash joins. This option is enabled by default. Drill
assumes that a query will have adequate memory to complete and tries to use the
fastest operations possible. Prior to Drill 1.14, the Hash-Join operator used
an uncontrolled amount of memory (up to 10 GB), after which the operator ran
out of memory. As of Drill 1.14, this operator can spill to disk. This option
is enabled by default. </p></li>
<li><p><strong>planner.enable_semijoin</strong><br>
-Enables or disables semi-joins. This option is enabled by default and only
works when the <code>planner.enable_hashjoin</code> option is also enabled.
When enabled, Drill uses semi-joins to remove the distinct processing below the
Hash Join and sets the semi-join flag in the Hash Join flag, as shown in the
following example: </p></li>
+Enables or disables semi-join functionality inside the Hash Join. This option
is enabled by default. When enabled, a semi-join flag inside the HashJoin flag
is set to true, and Drill uses a semi-join to remove the distinct processing
below the Hash Join. When disabled, Drill can still perform semi-joins, but the
semi-joins are performed outside of the Hash Join, as shown in the following
example: </p></li>
</ul>
<h3 id="example-query-plan-with-and-without-semi-join">Example: Query Plan
with and without Semi-Join</h3>
@@ -1425,9 +1425,11 @@ planner.enable_semijoin
</code></pre></div>
<p><strong>Semi-Join Enabled</strong><br>
In the following query plan, you can see that the HashAgg is absent. In the
HashJoin flag, you can see that semi-join flag is set to true, indicating that
a semi-join was used. Using the semi-join optimizes the query by reducing the
amount of processing that Drill must perform on data. </p>
-<div class="highlight"><pre><code class="language-text"
data-lang="text">EXPLAIN PLAN FOR SELECT employee_id, full_name FROM
cp.`employee.json` WHERE employee_id IN (SELECT employee_id FROM
cp.`employee.json`);
---------------------------------------------------------------------------------+
-| text
|
+----------------------------------------------------------------------------------+
+<div class="highlight"><pre><code class="language-text"
data-lang="text">EXPLAIN PLAN FOR SELECT employee_id, full_name FROM
cp.`employee.json` WHERE employee_id IN (SELECT employee_id FROM
cp.`employee.json`);
+
++----------------------------------------------------------------------------------+----------------------------------------------------------------------------------+
+| text
|
++----------------------------------------------------------------------------------+----------------------------------------------------------------------------------+
| 00-00 Screen
00-01 Project(employee_id=[$0], full_name=[$1])
00-02 HashJoin(condition=[=($0, $2)], joinType=[inner], semi-join:
=[true])
diff --git a/feed.xml b/feed.xml
index 0d3ebf0..a850376 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>Thu, 20 Dec 2018 15:39:02 -0800</pubDate>
- <lastBuildDate>Thu, 20 Dec 2018 15:39:02 -0800</lastBuildDate>
+ <pubDate>Thu, 20 Dec 2018 18:21:08 -0800</pubDate>
+ <lastBuildDate>Thu, 20 Dec 2018 18:21:08 -0800</lastBuildDate>
<generator>Jekyll v2.5.2</generator>
<item>
