SQL: counters for rows read and written#979
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Does this patch come directly from libSQL? If so we need to include license and copyright information, probably in the description header for each patch file. (Looks like it's MIT license, so no issues using it, but still need to include the copyright.) |
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The patch now contains an appropriate copyright header pointing at libsql. |
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| auto& query = state.query; | ||
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| obj->rowsRead = query.getRowsRead(); |
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Hmm, it seems wasteful to query these counters on every single row even if the app doesn't ever use them. (And even apps that do use them probably wouldn't check them on every row.)
Maybe we could have the implementation of getRowsRead() delegate to the underlying Query if it is still active. Then we only need to make a copy when the query is done.
Or maybe this isn't expensive enough to matter?
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They're cheap enough that this probably doesn't matter, but I agree that it looks wasteful, which is a trap for future programmers to fall into.
I took your suggestion of saving them off when the Query is done. I didn't see a way of invalidating a query out from under a Cursor, but if you know of one, then please tell me because that'll make the cursor falsely report 0 for row counts.
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This takes the row-counting logic from libsql[1] and sticks it into
our copy of SQLite.
libsql is an ambitious fork of SQLite, so switching out the entire
library would be quite risky. Porting the row-counting logic from
libsql (which is MIT-licensed) is a much less risky change, though it
does require us to carry a patch around forever, or at least until
SQLite implements something similar, if they ever do.
[1] A fork of sqlite that accepts contributions.
https://github.com/libsql/libsql
The `storage.sql` object in JS now has two new properties: `rowsRead` and `rowsWritten`, which contain appropriate numbers. Similarly, workerd::api::SqliteDatabase::getRows[Read|Written] provide the same numbers in C++. The counters are only updated after a full result set has been read. I thought about updating the counters as each row was read, but that has the disadvantage of counting rows that weren't useful due to errors. If one wanted to meter usage based on rows, one would only want to count rows for successfully-executed queries.
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In a durable object, state.storage.sql now has two new properties: rowsRead and rowsWritten. These count the number of rows read and written by the underlying SQLite database.
This is more than just the number of rows returned from queries or the number of records inserted/updated; it counts all rows read by the database engine in the processing of a query. For example, SELECT MAX(unindexed_column) FROM a_table returns a single result but reads every row from disk, and rowsRead reflects that.