22.9. Compressed storage of short strings
Neo4j will try to classify your strings in a short string class and if it manages that it will treat it accordingly. In that case, it will be stored without indirection in the property store, inlining it instead in the property record, meaning that the dynamic string store will not be involved in storing that value, leading to reduced disk footprint. Additionally, when no string record is needed to store the property, it can be read and written in a single lookup, leading to performance improvements and less disk space required.
The various classes for short strings are:
- Numerical, consisting of digits 0..9 and the punctuation space, period, dash, plus, comma and apostrophe.
- Date, consisting of digits 0..9 and the punctuation space dash, colon, slash, plus and comma.
- Hex (lower case), consisting of digits 0..9 and lower case letters a..f
- Hex (upper case), consisting of digits 0..9 and upper case letters a..f
- Upper case, consisting of upper case letters A..Z, and the punctuation space, underscore, period, dash, colon and slash.
- Lower case, like upper but with lower case letters a..z instead of upper case
- E-mail, consisting of lower case letters a..z and the punctuation comma, underscore, period, dash, plus and the at sign (@).
- URI, consisting of lower case letters a..z, digits 0..9 and most punctuation available.
- Alpha-numerical, consisting of both upper and lower case letters a..zA..z, digits 0..9 and punctuation space and underscore.
- Alpha-symbolical, consisting of both upper and lower case letters a..zA..Z and the punctuation space, underscore, period, dash, colon, slash, plus, comma, apostrophe, at sign, pipe and semicolon.
- European, consisting of most accented european characters and digits plus punctuation space, dash, underscore and period — like latin1 but with less punctuation.
- Latin 1.
In addition to the string’s contents, the number of characters also determines if the string can be inlined or not. Each class has its own character count limits, which are
Character count limits
|String class||Character count limit|
Numerical, Date and Hex
Uppercase, Lowercase and E-mail
URI, Alphanumerical and Alphasymbolical
That means that the largest inline-able string is 54 characters long and must be of the Numerical class and also that all Strings of size 14 or less will always be inlined.
Also note that the above limits are for the default 41 byte PropertyRecord layout — if that parameter is changed via editing the source and recompiling, the above have to be recalculated.