Use a marker file when removing a plugin #24252
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Today when removing a plugin, we attempt to move the plugin directory to a temporary directory and then delete that directory from the filesystem. We do this to avoid a plugin being in a half-removed state. We previously tried an atomic move, and fell back to a non-atomic move if that failed. Atomic moves can fail on union filesystems when the plugin directory is not in the top layer of the filesystem. Interestingly, the regular move can fail as well. This is because when the JDK is executing such a move, it first tries to rename the source directory to the target directory and if this fails with EXDEV (as in the case of an atomic move failing), it falls back to copying the source to the target, and then attempts to rmdir the source. The bug here is that the JDK never deleted the contents of the source so the rmdir will always fail (except in the case of an empty directory). Given all this silliness, we were inspired to find a different strategy. The strategy is simple. We will add a marker file to the plugin directory that indicates the plugin is in a state of removal. This file will be the last file out the door during removal. If this file exists during startup, we fail startup.
jasontedor
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jasontedor
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Apr 21, 2017
Today when removing a plugin, we attempt to move the plugin directory to a temporary directory and then delete that directory from the filesystem. We do this to avoid a plugin being in a half-removed state. We previously tried an atomic move, and fell back to a non-atomic move if that failed. Atomic moves can fail on union filesystems when the plugin directory is not in the top layer of the filesystem. Interestingly, the regular move can fail as well. This is because when the JDK is executing such a move, it first tries to rename the source directory to the target directory and if this fails with EXDEV (as in the case of an atomic move failing), it falls back to copying the source to the target, and then attempts to rmdir the source. The bug here is that the JDK never deleted the contents of the source so the rmdir will always fail (except in the case of an empty directory). Given all this silliness, we were inspired to find a different strategy. The strategy is simple. We will add a marker file to the plugin directory that indicates the plugin is in a state of removal. This file will be the last file out the door during removal. If this file exists during startup, we fail startup. Relates #24252
jasontedor
added a commit
that referenced
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Apr 21, 2017
Today when removing a plugin, we attempt to move the plugin directory to a temporary directory and then delete that directory from the filesystem. We do this to avoid a plugin being in a half-removed state. We previously tried an atomic move, and fell back to a non-atomic move if that failed. Atomic moves can fail on union filesystems when the plugin directory is not in the top layer of the filesystem. Interestingly, the regular move can fail as well. This is because when the JDK is executing such a move, it first tries to rename the source directory to the target directory and if this fails with EXDEV (as in the case of an atomic move failing), it falls back to copying the source to the target, and then attempts to rmdir the source. The bug here is that the JDK never deleted the contents of the source so the rmdir will always fail (except in the case of an empty directory). Given all this silliness, we were inspired to find a different strategy. The strategy is simple. We will add a marker file to the plugin directory that indicates the plugin is in a state of removal. This file will be the last file out the door during removal. If this file exists during startup, we fail startup. Relates #24252
jasontedor
added a commit
that referenced
this pull request
Apr 21, 2017
Today when removing a plugin, we attempt to move the plugin directory to a temporary directory and then delete that directory from the filesystem. We do this to avoid a plugin being in a half-removed state. We previously tried an atomic move, and fell back to a non-atomic move if that failed. Atomic moves can fail on union filesystems when the plugin directory is not in the top layer of the filesystem. Interestingly, the regular move can fail as well. This is because when the JDK is executing such a move, it first tries to rename the source directory to the target directory and if this fails with EXDEV (as in the case of an atomic move failing), it falls back to copying the source to the target, and then attempts to rmdir the source. The bug here is that the JDK never deleted the contents of the source so the rmdir will always fail (except in the case of an empty directory). Given all this silliness, we were inspired to find a different strategy. The strategy is simple. We will add a marker file to the plugin directory that indicates the plugin is in a state of removal. This file will be the last file out the door during removal. If this file exists during startup, we fail startup. Relates #24252
asettouf
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Apr 23, 2017
Today when removing a plugin, we attempt to move the plugin directory to a temporary directory and then delete that directory from the filesystem. We do this to avoid a plugin being in a half-removed state. We previously tried an atomic move, and fell back to a non-atomic move if that failed. Atomic moves can fail on union filesystems when the plugin directory is not in the top layer of the filesystem. Interestingly, the regular move can fail as well. This is because when the JDK is executing such a move, it first tries to rename the source directory to the target directory and if this fails with EXDEV (as in the case of an atomic move failing), it falls back to copying the source to the target, and then attempts to rmdir the source. The bug here is that the JDK never deleted the contents of the source so the rmdir will always fail (except in the case of an empty directory). Given all this silliness, we were inspired to find a different strategy. The strategy is simple. We will add a marker file to the plugin directory that indicates the plugin is in a state of removal. This file will be the last file out the door during removal. If this file exists during startup, we fail startup. Relates elastic#24252
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Today when removing a plugin, we attempt to move the plugin directory to a temporary directory and then delete that directory from the filesystem. We do this to avoid a plugin being in a half-removed state. We previously tried an atomic move, and fell back to a non-atomic move if that failed. Atomic moves can fail on union filesystems when the plugin directory is not in the top layer of the filesystem. Interestingly, the regular move can fail as well. This is because when the JDK is executing such a move, it first tries to rename the source directory to the target directory and if this fails with EXDEV (as in the case of an atomic move failing), it falls back to copying the source to the target, and then attempts to rmdir the source. The bug here is that the JDK never deleted the contents of the source so the rmdir will always fail (except in the case of an empty directory).
Given all this silliness, we were inspired to find a different strategy. The strategy is simple. We will add a marker file to the plugin directory that indicates the plugin is in a state of removal. This file will be the last file out the door during removal. If this file exists during startup, we fail startup.
Closes #24231