From: Eric Wong <e@yhbt.net>
Date: Sun, 10 May 2020 22:37:13 +0000 (+0000)
Subject: overidx: document the SQLite PRAGMA we use
X-Git-Tag: v1.6.0~505
X-Git-Url: http://www.git.stargrave.org/?a=commitdiff_plain;h=5ce52f3dd831c623b8899dc4d5655c2d958fa6a0;p=public-inbox.git

overidx: document the SQLite PRAGMA we use

This ought to prevent cargo-culting the cache_size PRAGMA
into smaller SQLite DBs we might use.
---

diff --git a/lib/PublicInbox/OverIdx.pm b/lib/PublicInbox/OverIdx.pm
index acbf2c8d..cb15baad 100644
--- a/lib/PublicInbox/OverIdx.pm
+++ b/lib/PublicInbox/OverIdx.pm
@@ -21,8 +21,16 @@ use PublicInbox::Search;
 sub dbh_new {
 	my ($self) = @_;
 	my $dbh = $self->SUPER::dbh_new(1);
+
+	# TRUNCATE reduces I/O compared to the default (DELETE)
 	$dbh->do('PRAGMA journal_mode = TRUNCATE');
+
+	# 80000 pages (80MiB on SQLite <3.12.0, 320MiB on 3.12.0+)
+	# was found to be good in 2018 during the large LKML import
+	# at the time.  This ought to be configurable based on HW
+	# and inbox size; I suspect it's overkill for many inboxes.
 	$dbh->do('PRAGMA cache_size = 80000');
+
 	create_tables($dbh);
 	$dbh;
 }