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authorSverker Eriksson <[email protected]>2019-02-15 16:42:33 +0100
committerGitHub <[email protected]>2019-02-15 16:42:33 +0100
commit77cff6693158dc2ab20b798db9c124a2c82f5e2a (patch)
tree96e7977b0052a2b562db6170e61e3c0791bfac23
parent1808e847e27456ac998aa686b18fd566bd9ffc24 (diff)
parent7e05835aa76645635ab6f1471c779adf4accb827 (diff)
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Merge PR-2139 from sverker/ets-doc-partially-bound-key/OTP-15545
Add ETS docs about partially bound key traversal
-rw-r--r--lib/stdlib/doc/src/ets.xml15
1 files changed, 15 insertions, 0 deletions
diff --git a/lib/stdlib/doc/src/ets.xml b/lib/stdlib/doc/src/ets.xml
index ccccf7de88..622edc072e 100644
--- a/lib/stdlib/doc/src/ets.xml
+++ b/lib/stdlib/doc/src/ets.xml
@@ -188,6 +188,21 @@
is used to keep the table fixated during the entire traversal.</p>
</item>
</list>
+ <p>Traversals using <c>match</c> and <c>select</c> functions may not need to
+ scan the entire table depending on how the key is specified. A match
+ pattern with a <em>fully bound key</em> (without any match variables) will
+ optimize the operation to a single key lookup without any table traversal
+ at all. For <c>ordered_set</c> a <em>partially bound key</em> will limit the
+ traversal to only scan a subset of the table based on term order. A
+ partially bound key is either a list or a tuple with a prefix that is fully
+ bound. Example:</p>
+<pre>
+1> <input>T = ets:new(t,[ordered_set]), ets:insert(T, {"555-1234", "John Smith"}).</input>
+true
+2> <input>%% Efficient search of all with area code 555</input>
+2> <input>ets:match(T,{[$5,$5,$5,$- |'$1'],'$2'}).</input>
+[["1234","John Smith"]]
+</pre>
</section>
<section>