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<channel>
    <title>MongoDB Jira</title>
    <link>https://jira.mongodb.org</link>
    <description>This file is an XML representation of an issue</description>
    <language>en-us</language>    <build-info>
        <version>9.7.1</version>
        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
    </build-info>


<item>
            <title>[SERVER-9856] No check for building identical background indexes concurrently</title>
                <link>https://jira.mongodb.org/browse/SERVER-9856</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;div class=&quot;panel&quot; style=&quot;background-color: #EEEEEE;border-color: #ccc;border-width: 1px;&quot;&gt;&lt;div class=&quot;panelHeader&quot; style=&quot;border-bottom-width: 1px;border-bottom-color: #ccc;background-color: #6CB33F;&quot;&gt;&lt;b&gt;Issue Status as of Sep 19, 2014&lt;/b&gt;&lt;/div&gt;&lt;div class=&quot;panelContent&quot; style=&quot;background-color: #EEEEEE;&quot;&gt;
&lt;p&gt;&lt;b&gt;ISSUE SUMMARY&lt;/b&gt;&lt;br/&gt;
It is possible to build duplicate indexes on a collection when indexes are run in the background, thus causing index corruption. Running &lt;tt&gt;db.repairDatabase()&lt;/tt&gt; fixes the index corruption.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;USER IMPACT&lt;/b&gt;&lt;br/&gt;
When a collection with duplicate indexes is dropped, or one of the duplicate indexes is dropped, users may encounter an error message similar to the following:&lt;/p&gt;

&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
		&lt;tbody &gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;Tue Jun  4 15:19:47.778 JavaScript execution failed: drop failed: {&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;        &quot;nIndexesWas&quot; : 2,&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;        &quot;errmsg&quot; : &quot;exception: drop: dropIndexes for collection failed - consider trying repair  cause: BSONObj size: 0 (0x00000000) is invalid. Size must be between 0 and 16793600(16MB) First element: EOO&quot;,&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;        &quot;code&quot; : 12503,&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;        &quot;ok&quot; : 0&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;}&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;

&lt;p&gt;When upgrading to MongoDB 2.6.x, this index corruption is detected during the startup sequence and the server aborts as follows:&lt;/p&gt;

&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
		&lt;tbody &gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;2014-10-15T12:17:47.641-0400 [IndexRebuilder] test.foo Invariant failure save == _entries.find( descriptor-&amp;gt;indexName() ) src/mongo/db/catalog/index_catalog.cpp 156&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;2014-10-15T12:17:47.644-0400 [IndexRebuilder] test.foo 0x1006ac7ab 0x1006642c2 0x100653fc9 0x1000f5e02 0x1000f7d0f 0x1000df14a 0x1000e538e 0x1002936ef 0x100293111 0x100656f8b 0x1006e0bb5 0x7fff8b44f899 0x7fff8b44f72a 0x7fff8b453fc9 &lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; 0   mongod                              0x00000001006ac7ab _ZN5mongo15printStackTraceERSo + 43&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; 1   mongod                              0x00000001006642c2 _ZN5mongo10logContextEPKc + 114&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; 2   mongod                              0x0000000100653fc9 _ZN5mongo15invariantFailedEPKcS1_j + 233&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; 3   mongod                              0x00000001000f5e02 _ZN5mongo12IndexCatalog24_setupInMemoryStructuresEPNS_15IndexDescriptorE + 748&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; 4   mongod                              0x00000001000f7d0f _ZN5mongo12IndexCatalog4initEv + 873&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; 5   mongod                              0x00000001000df14a _ZN5mongo10CollectionC2ERKNS_10StringDataEPNS_16NamespaceDetailsEPNS_8DatabaseE + 756&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; 6   mongod                              0x00000001000e538e _ZN5mongo8Database13getCollectionERKNS_10StringDataE + 322&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; 7   mongod                              0x00000001002936ef _ZN5mongo14IndexRebuilder7checkNSERKSt4listISsSaISsEE + 317&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; 8   mongod                              0x0000000100293111 _ZN5mongo14IndexRebuilder3runEv + 399&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; 9   mongod                              0x0000000100656f8b _ZN5mongo13BackgroundJob7jobBodyEv + 257&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; 10  mongod                              0x00000001006e0bb5 thread_proxy + 229&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; 11  libsystem_pthread.dylib             0x00007fff8b44f899 _pthread_body + 138&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; 12  libsystem_pthread.dylib             0x00007fff8b44f72a _pthread_struct_init + 0&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; 13  libsystem_pthread.dylib             0x00007fff8b453fc9 thread_start + 13&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;2014-10-15T12:17:47.644-0400 [IndexRebuilder] &lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&amp;nbsp;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;***aborting after invariant() failure&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;

&lt;p&gt;&lt;b&gt;WORKAROUNDS&lt;/b&gt;&lt;br/&gt;
The recommended workaround for users running a replica set is to shut down the affected node and &lt;a href=&quot;http://docs.mongodb.org/manual/tutorial/resync-replica-set-member/#resync-a-member-of-a-replica-set&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;resync the node from the primary&lt;/a&gt;.&lt;/p&gt;

&lt;p&gt;Users running a standalone server may &lt;a href=&quot;http://docs.mongodb.org/manual/tutorial/convert-standalone-to-replica-set/#convert-a-standalone-to-a-replica-set&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;temporarily convert the standalone node to a replica set&lt;/a&gt;, then add a new node to the replica set. Once the new node has finished its initial sync, shut it down and restart it as a standalone instance, and manually build the indexes that were corrupted on the primary. The new instance should now be used instead of the original one.&lt;/p&gt;

&lt;p&gt;Alternatively, standalone servers can be recovered by running  &lt;a href=&quot;http://docs.mongodb.org/manual/reference/command/repairDatabase/#repairdatabase&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;&lt;tt&gt;repairDatabase()&lt;/tt&gt;&lt;/a&gt; using a 2.4-series MongoDB version 2.4.5 or older. Then it is safe to upgrade to MongoDB 2.6. If running MongoDB 2.4 is preferred, it is highly recommended to upgrade to the latest 2.4.x release.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;AFFECTED VERSIONS&lt;/b&gt;&lt;br/&gt;
MongoDB 2.4 production releases up to 2.4.4 are affected by this issue.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;FIX VERSION&lt;/b&gt;&lt;br/&gt;
The fix is included in the 2.4.5 production release.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;RESOLUTION DETAILS&lt;/b&gt;&lt;br/&gt;
Check in-progress indexes for duplicates in prepareToBuildIndex().&lt;/p&gt;
&lt;/div&gt;&lt;/div&gt;

&lt;h6&gt;&lt;a name=&quot;Originaldescription&quot;&gt;&lt;/a&gt;Original description&lt;/h6&gt;

&lt;p&gt;Since 2.4 it is possible to build background indexes concurrently. There is no check if that index is the same one, which can lead to a situation where the same index exists multiple times on a collection.&lt;/p&gt;

&lt;p&gt;Trying to drop that index, or all indexes, or the collection leads to this error:&lt;/p&gt;

&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
		&lt;tbody &gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;Tue Jun  4 15:19:47.778 JavaScript execution failed: drop failed: {&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;        &quot;nIndexesWas&quot; : 2,&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;        &quot;errmsg&quot; : &quot;exception: drop: dropIndexes for collection failed - consider trying repair  cause: BSONObj size: 0 (0x00000000) is invalid. Size must be between 0 and 16793600(16MB) First element: EOO&quot;,&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
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						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;        &quot;code&quot; : 12503,&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
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			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;}&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;

&lt;p&gt;Subsequent queries using the half-dropped index will result in errors as well.&lt;/p&gt;

&lt;p&gt;In 2.4.x, the secondaries were unaffected by this because we didn&apos;t allow background index builds on secondaries. The index was only present once on the secondary. In 2.5.0 the duplicate index carries over to the secondaries and show the same behavior as the primaries.&lt;/p&gt;

&lt;p&gt;This is a regression from 2.2 where a second background index build was not allowed and therefore the bug could not occur.&lt;/p&gt;

&lt;p&gt;A db.repairDatabase() seems to fix the problem.&lt;/p&gt;</description>
                <environment></environment>
        <key id="77758">SERVER-9856</key>
            <summary>No check for building identical background indexes concurrently</summary>
                <type id="1" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14703&amp;avatarType=issuetype">Bug</type>
                                            <priority id="2" iconUrl="https://jira.mongodb.org/images/icons/priorities/critical.svg">Critical - P2</priority>
                        <status id="6" iconUrl="https://jira.mongodb.org/images/icons/statuses/closed.png" description="The issue is considered finished, the resolution is correct. Issues which are closed can be reopened.">Closed</status>
                    <statusCategory id="3" key="done" colorName="success"/>
                                    <resolution id="9">Done</resolution>
                                        <assignee username="milkie@mongodb.com">Eric Milkie</assignee>
                                    <reporter username="thomas.rueckstiess@mongodb.com">Thomas Rueckstiess</reporter>
                        <labels>
                    </labels>
                <created>Tue, 4 Jun 2013 05:31:53 +0000</created>
                <updated>Mon, 11 Jul 2016 17:40:24 +0000</updated>
                            <resolved>Mon, 10 Jun 2013 13:38:42 +0000</resolved>
                                    <version>2.4.4</version>
                    <version>2.5.0</version>
                                    <fixVersion>2.4.5</fixVersion>
                    <fixVersion>2.5.1</fixVersion>
                                    <component>Index Maintenance</component>
                                        <votes>4</votes>
                                    <watches>16</watches>
                                                                                                                <comments>
                            <comment id="371667" author="dan@10gen.com" created="Mon, 1 Jul 2013 15:12:21 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=chengas123&quot; class=&quot;user-hover&quot; rel=&quot;chengas123&quot;&gt;chengas123&lt;/a&gt;, we don&apos;t have a quick fix available to remove the extra indexes at this point other than doing a repair database.  There are a couple of  alternatives:&lt;/p&gt;

&lt;ul&gt;
	&lt;li&gt;If you are running with a replica set, there is a possible workaround.  In version 2.4, secondaries do not allow indexes to be built in the background, even if they were built in the background on the primary. Thus, secondaries should have no duplicate indexes.  As an alternative to running db.repairDatabase on your primary, you can promote your secondary to primary and completely resync your old primary from scratch.&lt;/li&gt;
	&lt;li&gt;You can run repairDatabase even if you have low disk space by using another disk for the repair target. Shut down the server and then run: &lt;tt&gt;mongod --repair --repairpath &amp;lt;some other mount point&amp;gt;&lt;/tt&gt;&lt;/li&gt;
&lt;/ul&gt;
</comment>
                            <comment id="371409" author="wiliam" created="Mon, 1 Jul 2013 07:03:22 +0000"  >&lt;p&gt;That would be great Ben McCann, repairDatabase is a expensive task y large databases.&lt;/p&gt;</comment>
                            <comment id="371403" author="chengas123" created="Mon, 1 Jul 2013 06:55:22 +0000"  >&lt;p&gt;Can you guys also add a fix to allow proper deletion of the multiple indexes? My disk is 60% used, so I will not be able to run db.repairDatabase()&lt;/p&gt;</comment>
                            <comment id="363799" author="auto" created="Wed, 19 Jun 2013 23:50:00 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;milkie&apos;, u&apos;name&apos;: u&apos;Eric Milkie&apos;, u&apos;email&apos;: u&apos;milkie@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-9856&quot; title=&quot;No check for building identical background indexes concurrently&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-9856&quot;&gt;&lt;del&gt;SERVER-9856&lt;/del&gt;&lt;/a&gt; check in-progress indexes for duplicates in prepareToBuildIndex()&lt;br/&gt;
Branch: v2.4&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/af0b49cbb0ca6888d6f133081b7d41464bf4135f&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/af0b49cbb0ca6888d6f133081b7d41464bf4135f&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="356769" author="auto" created="Mon, 10 Jun 2013 13:38:00 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;milkie&apos;, u&apos;name&apos;: u&apos;Eric Milkie&apos;, u&apos;email&apos;: u&apos;milkie@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-9856&quot; title=&quot;No check for building identical background indexes concurrently&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-9856&quot;&gt;&lt;del&gt;SERVER-9856&lt;/del&gt;&lt;/a&gt; check in-progress indexes for duplicates in prepareToBuildIndex()&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/1e65ddf0bf4fe11d2ab71cf04be808e9a10f342d&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/1e65ddf0bf4fe11d2ab71cf04be808e9a10f342d&lt;/a&gt;&lt;/p&gt;</comment>
                    </comments>
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	&lt;li&gt;insert large number of documents into a primary&lt;/li&gt;
	&lt;li&gt;open two shells, start background index build of same index in both shells&lt;/li&gt;
	&lt;li&gt;confirm with db.collection.getIndexes() that there are multiple identical indexes&lt;/li&gt;
&lt;/ol&gt;


&lt;p&gt;Everything seems to work ok, until you&lt;/p&gt;

&lt;ul&gt;
	&lt;li&gt;try to drop the index with db.collection.dropIndex(&amp;lt;index&amp;gt;)&lt;/li&gt;
	&lt;li&gt;try to drop all indexes with db.collection.dropIndexes()&lt;/li&gt;
	&lt;li&gt;try to drop the collection with db.collection.drop()&lt;/li&gt;
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&lt;p&gt;After one of these operations, even hinting on that particular index fails with the same error. It seems the index does get deleted but not properly cleaned up.&lt;/p&gt;</customfieldvalue>

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