Development Team/Datastore Rewrite: Difference between revisions

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<noinclude>{{ GoogleTrans-en | es =show | bg =show | zh-CN =show | zh-TW =show | hr =show | cs =show | da =show | nl =show | fi =show | fr =show | de =show | el =show | hi =show | it =show | ja =show | ko =show | no =show | pl =show | pt =show | ro =show | ru =show | sv =show }}</noinclude>

== Introduction ==

This page describes the design of a new DataStore implementation that was shipped first in the [[0.84]] (April 2009) Sugar release.

== Goals ==

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By examining the directory structure, we know where is localized the data related to each entry. We don't depend any more on a binary structure that could become corrupted and unusable as a whole.

=== Metadata is stored as a single file ~~for each entry~~ ===

=== Metadata is stored in a single file per property ===

~~Each~~ entry ~~has its metadata~~ stored in ~~a single file~~, ~~so that~~ if corruption happened on one of those, the rest of the entries would be unaffected. ~~The format in which metadata is stored even allows to recover from a malformed property by just dropping it~~.

Metadata for each entry is stored in several files, one per property. In this way, if corruption happened on one those properties, the rest of the entry (and the other entries in the DS) would be unaffected.

: See [[olpc:Low-level_Activity_API#Meta_Data]].

=== Queries are accelerated with a disposable database ===

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1a

1ab88287-766a-4d98-a7c0-4233dc48647a

~~1ab88287~~-~~766a-4d98-a7c0-4233dc48647a~~

data

~~metadata~~

metadata

uid

checksum

activity_id

mime_type

preview

share-scope

timestamp

title

2b

2b90597c-0912-4e7f-8eeb-71a0f004490d

~~2b90597c-0912-4e7f-8eeb-71a0f004490d -> checksums/464493d8d929436b6152e868867ed451~~

data

checksum ~~~> checksums/464493d8d929436b6152e868867ed451~~

metadata

~~extra_metadata~~

uid

preview

checksum

~~metadata~~

activity_id

mime_type

preview

share-scope

timestamp

title

3c

3cdf5f0e-7595-4166-b1f9-cbedfcfe1c4a

~~3cdf5f0e~~-~~7595~~-~~4166~~-~~b1f9~~-~~cbedfcfe1c4a~~ -~~> checksums~~/~~464493d8d929436b6152e868867ed451~~

data -> 2b/2b90597c-0912-4e7f-8eeb-71a0f004490d/data

checksum ~~~> checksums/464493d8d929436b6152e868867ed451~~

metadata

~~extra_metadata~~

uid

preview

checksum

~~metadata~~

activity_id

mime_type

preview

share-scope

timestamp

title

4d

4db11d29-2f07-4452-bd8e-22a6a483ac19

~~4db11d29-2f07-4452-bd8e-22a6a483ac19~~

data

~~metadata~~

metadata

~~extra_metadata~~

uid

preview

checksum

5e

activity_id

~~5e9f2027~~-b41e-4015-a848-6b3972193eb8

mime_type

~~5e9f2027-b41e-4015-a848-6b3972193eb8~~

preview

~~metadata~~

share-scope

~~extra_metadata~~

timestamp

preview

title

4d9f2027-b41e-4015-a848-6b3972193eb8

data

metadata

uid

checksum

activity_id

mime_type

preview

share-scope

timestamp

title

checksums

464493d8d929436b6152e868867ed451

~~2b90597c-0912-4e7f-8eeb-71a0f004490d ~> 2b90597c-0912-4e7f-8eeb-71a0f004490d/~~2b90597c-0912-4e7f-8eeb-71a0f004490d

2b90597c-0912-4e7f-8eeb-71a0f004490d

~~3cdf5f0e-7595-4166-b1f9-cbedfcfe1c4a ~> 3cdf5f0e-7595-4166-b1f9-cbedfcfe1c4a/~~3cdf5f0e-7595-4166-b1f9-cbedfcfe1c4a

3cdf5f0e-7595-4166-b1f9-cbedfcfe1c4a

index

flintlock

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value.baseB

value.DB

index_updated

version

'''1a''': directory holding entries, it's only function is to avoid having too many directories in a single directory, as this is considered specially harmful on jffs2.

'''1a/1ab88287-...-4233dc48647a''': directory holding the files related to one entry

'''1a/1ab88287-...-4233dc48647a/data''': file related to an entry

'''1a/1ab88287-...-4233dc48647a/metadata''': directory containing a file for each metadata property of an entry

'''2b/2b90597c-...-71a0f004490d/metadata/activity_id''': file containing the value of the '''activity_id''' property

'''3c/3cdf5f0e-...-cbedfcfe1c4a/data''': hard link to the same file in the entry '''2b90597c-...-71a0f004490d'''

'''checksums''': directory containing a directory per each file contained in the DS, named by its md5 checksum

'''checksums/464493d8d929436b6152e868867ed451''': directory containing files named by each entry that contain a file with this checksum

'''checksums/464493d8d929436b6152e868867ed451/2b90597c-...-71a0f004490d''' file named by the uid of an entry the file of which has this checksum.

'''index''': directory containing all files that belong to the search database. Can be deleted and recreated from the rest of the DS if needed without incurring in data loss.

'''index_updated''': When this file is not present, is because the xapian index is being rebuilt because it cannot be opened. Queries should fall back to display all the files on disk until the index is rebuilt.

'''version''': file that contains the version of the file layout. Currently we are at 1. Is updated when an earlier version is migrated to a newer one.

== Source code ==

http://~~dev~~.~~laptop~~.org/~~git?p=users/tomeu~~/datastore~~;a=summary~~

http://git.sugarlabs.org/projects/sugar-datastore

@@ Line 1: / Line 1: @@
+<noinclude>{{ GoogleTrans-en | es =show | bg =show | zh-CN =show | zh-TW =show | hr =show | cs =show | da =show | nl =show | fi =show | fr =show | de =show | el =show | hi =show | it =show | ja =show | ko =show | no =show | pl =show | pt =show | ro =show | ru =show | sv =show }}</noinclude>
+{{TOCright}}
+== Introduction ==
+This page describes the design of a new DataStore implementation that was shipped first in the [[0.84]] (April 2009) Sugar release.
 == Goals ==
@@ Line 35: / Line 42: @@
 By examining the directory structure, we know where is localized the data related to each entry. We don't depend any more on a binary structure that could become corrupted and unusable as a whole.
-=== Metadata is stored as a single file for each entry ===
+=== Metadata is stored in a single file per property ===
-Each entry has its metadata stored in a single file, so that if corruption happened on one of those, the rest of the entries would be unaffected. The format in which metadata is stored even allows to recover from a malformed property by just dropping it.
+Metadata for each entry is stored in several files, one per property. In this way, if corruption happened on one those properties, the rest of the entry (and the other entries in the DS) would be unaffected.
+: See [[olpc:Low-level_Activity_API#Meta_Data]].
 === Queries are accelerated with a disposable database ===
@@ Line 55: / Line 63: @@
 a
 ab88287-766a-4d98-a7c0-4233dc48647a
-ab88287-766a-4d98-a7c0-4233dc48647a
+              data
-                    metadata
+             metadata
+                   uid
+                   checksum
+                   activity_id
+                   mime_type
+                   preview
+                   share-scope
+                   timestamp
+                    title
 b
 b90597c-0912-4e7f-8eeb-71a0f004490d
-b90597c-0912-4e7f-8eeb-71a0f004490d -> checksums/464493d8d929436b6152e868867ed451
+              data
-                    checksum ~> checksums/464493d8d929436b6152e868867ed451
+             metadata
-                    extra_metadata
+                   uid
-                         preview
+                    checksum
-                    metadata
+                    activity_id
+                   mime_type
+                   preview
+                    share-scope
+                   timestamp
+                   title
 c
 cdf5f0e-7595-4166-b1f9-cbedfcfe1c4a
-cdf5f0e-7595-4166-b1f9-cbedfcfe1c4a -> checksums/464493d8d929436b6152e868867ed451
+              data -> 2b/2b90597c-0912-4e7f-8eeb-71a0f004490d/data
-                    checksum ~> checksums/464493d8d929436b6152e868867ed451
+             metadata
-                    extra_metadata
+                   uid
-                         preview
+                    checksum
-                    metadata
+                    activity_id
+                   mime_type
+                   preview
+                    share-scope
+                   timestamp
+                   title
 d
 db11d29-2f07-4452-bd8e-22a6a483ac19
-db11d29-2f07-4452-bd8e-22a6a483ac19
+              data
-                    metadata
+             metadata
-                    extra_metadata
+                   uid
-                         preview
+                   checksum
-e
+                    activity_id
-e9f2027-b41e-4015-a848-6b3972193eb8
+                    mime_type
-e9f2027-b41e-4015-a848-6b3972193eb8
+                   preview
-                    metadata
+                   share-scope
-                    extra_metadata
+                   timestamp
-                         preview
+                   title
+d9f2027-b41e-4015-a848-6b3972193eb8
+              data
+             metadata
+                   uid
+                   checksum
+                    activity_id
+                    mime_type
+                   preview
+                   share-scope
+                   timestamp
+                   title
   checksums
 d8d929436b6152e868867ed451
-b90597c-0912-4e7f-8eeb-71a0f004490d ~> 2b90597c-0912-4e7f-8eeb-71a0f004490d/2b90597c-0912-4e7f-8eeb-71a0f004490d
+b90597c-0912-4e7f-8eeb-71a0f004490d
-cdf5f0e-7595-4166-b1f9-cbedfcfe1c4a ~> 3cdf5f0e-7595-4166-b1f9-cbedfcfe1c4a/3cdf5f0e-7595-4166-b1f9-cbedfcfe1c4a
+cdf5f0e-7595-4166-b1f9-cbedfcfe1c4a
   index
         flintlock
@@ Line 102: / Line 139: @@
         value.baseB
         value.DB
+ index_updated
+ version
+'''1a''': directory holding entries, it's only function is to avoid having too many directories in a single directory, as this is considered specially harmful on jffs2.
+'''1a/1ab88287-...-4233dc48647a''': directory holding the files related to one entry
+'''1a/1ab88287-...-4233dc48647a/data''': file related to an entry
+'''1a/1ab88287-...-4233dc48647a/metadata''': directory containing a file for each metadata property of an entry
+'''2b/2b90597c-...-71a0f004490d/metadata/activity_id''': file containing the value of the '''activity_id''' property
+'''3c/3cdf5f0e-...-cbedfcfe1c4a/data''': hard link to the same file in the entry '''2b90597c-...-71a0f004490d'''
+'''checksums''': directory containing a directory per each file contained in the DS, named by its md5 checksum
+'''checksums/464493d8d929436b6152e868867ed451''': directory containing files named by each entry that contain a file with this checksum
+'''checksums/464493d8d929436b6152e868867ed451/2b90597c-...-71a0f004490d''' file named by the uid of an entry the file of which has this checksum.
+'''index''': directory containing all files that belong to the search database. Can be deleted and recreated from the rest of the DS if needed without incurring in data loss.
+'''index_updated''': When this file is not present, is because the xapian index is being rebuilt because it cannot be opened. Queries should fall back to display all the files on disk until the index is rebuilt.
+'''version''': file that contains the version of the file layout. Currently we are at 1. Is updated when an earlier version is migrated to a newer one.
 == Source code ==
-http://dev.laptop.org/git?p=users/tomeu/datastore;a=summary
+http://git.sugarlabs.org/projects/sugar-datastore